DEPARTMENT OF CIVIL ENGINEERING CIV4044S. BSc Research Project. Prepared for Professor Neil Armitage, Lloyd Fisher-Jeffes, David Ellis

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1 DEPARTMENT OF CIVIL ENGINEERING CIV4044S BSc Research Project Evaluating the potential of selected WSUD measures in a generic middle income urban catchment in South Africa Prepared for Professor Neil Armitage, Lloyd Fisher-Jeffes, David Ellis Prepared by Aumashvini Gobin

2 I Plagiarism Declaration I know that plagiarism is wrong. Plagiarism is to use another s work and to pretend that it is one s own. I have used the Harvard Convention for citation and referencing. Each significant contribution to and quotation in this report form the work or works of other people has been attributed and has been cited and referenced. This report is our work. I have not allowed and will not allow anyone to copy my work with the intention of passing it as their own work. Name Student Number Signature Aumashvini Gobin GBNAUM001 Plagiarism Declaration

3 II Acknowledgement I would first like to thank my supervisor Professor Neil Armitage for guiding me, giving insights and useful comments throughout the research project. I would also like to express my deepest gratitude to Lloyd Fisher-Jeffes for helping at every step of the thesis, providing his models, indispensable information and data. To David Ellis, for his constant guidance and being available for any concerns and queries that I had and providing assistance and reviews for each draft. To my family and friends for their relentless support throughout the process. And finally to Weather SA, for providing valuable climatic information for the purpose of the study. Aclnowledgments

4 III Abstract South Africa is classified as a water scarce country with a mean annual rainfall of 490 mm which is half of the global average. Water resources are already stressed and demands for potable water are projected to increase by at least 17 % by 2030 with development and population growths. These facts call for urgent measures to be taken to decrease our dependency on fresh water sources and change the conventional linear and inefficient urban cycle to a more sustainable and cyclical one. The term Water Sensitive Settlements (WSS) represents this ideology and can be achieved through Water Sensitive Urban Design (WSUD) measures. These have enormous potential in improving the urban water cycle to reach the level of WSS. The research focuses on examining the effects of WSUD measures in middle income suburbs found in the City of Cape Town and compares the results of implementing the same measures in the other eight Metropolitan municipalities of the South African Cities Network (SACN). Gatesville and Surrey Estate, Cape Town were identified as the suburbs to be investigated and their demographical, climatic and billing data were used to calculate the total residential demand of the catchment which came up to be Ml/year. The data was cleared of any leakages and anomalies and each of the 1028 investigated residential properties indoor and outdoor demands were calculated. The outdoor demand accounted for 21 % of the total water demand (TWD). Four measures were identified; rainwater harvesting (RWH), greywater harvesting (GWH), the use of water efficient devices (WED) and on-site leakage management for the purpose of the study. These have adequate background information and are appropriate to be applied in an already developed area. Several scenarios were examined using each of the measures individually or combinations of them on each property. The demand met of each scenario increases as the demand for water supplied from particular system increase. The cost on the other hand, decreases as the demand met increases but this is the case for only individual application of each measure. The combined use of WED with RWH and GWH undermines the efficiency of each individual measure. WED decrease both the demand for rainwater for indoor devices and the flow of greywater from the same devices. The combined use of the measures despite resulting in reduction of almost 50 % of the water demands, have significantly higher costs ranging from 100 to 300 R/kl of water saved. The best fit scenarios are weighed as a compromise between demand met and the cost of implementation of each measure. The results for CT showed that WED have the highest savings amounting up to 87.4 Ml/year, followed by the use of greywater harvesting for garden irrigation only (42.5 Ml/year) and rainwater harvesting for both indoor and outdoor uses (52 Ml/year). On-site leakage management despite having savings of 0.8 Ml/year was found to decrease the water demand by less than 1 %. The results from the other cities show the variability of RWH and GWH systems efficiency in different climatic conditions. The competence of RWH systems depends Abstract

5 IV on the amount and the annual distribution of rainfall in an area. The efficiency of RWH scenarios increases up to 50 % in ethekwini compared to CT, having an annual rainfall of 980 mm. GWH system s trends show that its efficiency increases in drier climatic conditions since it is used only for outdoor purposes and has a more reliable source of water than RWH systems. The feasibility of individual systems is more appropriate for the given suburbs given their level of income, with the costs of the individual measures ranging from 40.2 to 82.5 R/kl. The current most economical solution for the catchment, with the cost of water being less than the water and sanitation tariffs is the GWH scenario for outdoor uses. With the rising costs of water and sanitation services, the implementation of WED and RWH can be considered as being cost effective in the coming 10 years with the current highest tariff blocks doubling and reaching 80 R/kl. As for the other cities investigated, the water and sanitation tariffs are smaller than that of Cape Town, decreasing the viability of implementing the measures even if the costs of implementation are lower than that of Cape Town. Abstract

6 V Table of Contents Plagiarism Declaration Acknowledgement Abstract Table of Contents List of Tables List of Figures List of acronyms I II III V VIII IX XI Introduction 1-1 Background to study 1-1 Problem statement 1-1 Aim and objectives 1-1 Scope & limitations of research project 1-2 Literature Review 2-1 Water scarcity in South Africa South African water usage Conventional urban water cycle Current and future challenges 2-3 Water Sensitive Urban Design WSC, WSS and the transitional framework Stakeholder involvement Challenges for the South African context Benefits of WSUD Overview of WSUD strategies 2-10 Potable water saving schemes Water losses- leakages Water efficient devices 2-13 Table of Contents

7 VI Alternative water sources 2-15 Modelling the benefits 2-17 Methodology 3-1 Data Collection Land Classification Calculation of capita per household Climate data 3-4 Water demand calculation Residential Indoor demand Outdoor demand 3-7 Calibration of calculated values Evaporation rates Residential AADD 3-9 URSHM 3-11 Water Demand Management (WDM) models Rainwater Harvesting Greywater Harvesting Water Efficient Devices (WED) On-site leakage management 3-15 Scenarios 3-16 Applicability of concept to other South African areas 3-18 Results 4-1 Catchment water usage 4-1 Cape Town Rainwater harvesting (RWH) Greywater harvesting (GWH) Water Efficient Devices Leakage Management Comparing the four measures Combinations 4-10 Table of Contents

8 VII Comparison between cities Demand met Cost efficiency 4-19 Final water balance Cape Town water tariffs ethekwini 4-26 Conclusion and Recommendations 5-1 References 6-1 Appendices Table of Contents

9 VIII List of Tables Table 2-1: Water allocation in SA (DWA, 2011) 2-1 Table 2-2: Area of interests for stakeholders (Armitage et al., 2014) 2-8 Table 3-1: Household counts 3-4 Table 3-2: Monthly Pan factors (Fisher- Jeffes, 2014) 3-8 Table 3-3: WED scenarios 3-14 Table 3-4: Leakage rates and occurrences 3-15 Table 3-5: Scenarios 3-17 Table 3-6: Major municipalities and associated station number 3-18 Table 4-1: RWH Scenarios 4-3 Table 4-2: GWH Scenarios 4-5 Table 4-3: Savings for high and medium ratios 4-6 Table 4-4: Combination Scenarios 4-11 Table 4-5: Annual Rainfall (Weather SA, 2014) 4-15 Table 4-6: Demand met for RWH scenarios 4-16 Table 4-7: Demand met for GWH scenarios 4-17 Table 4-8: Demand met for all nine cities' combined scenarios 4-18 Table 4-9: City of Cape Town water tariffs (CoCT, 2014) 4-24 List of Tables

10 IX List of Figures Figure 2-1: Natural &Urban water balances balances (Hoban & Wong, 2006) 2-2 Figure 2-2: Mirroring natural water cycle (Hoban & Wong, 2006) 2-5 Figure 2-3: Transition to WSC (Brown et al., 2008) 2-6 Figure 2-4: WSS Framework (Armitage et al., 2014) 2-7 Figure 2-5: WSUD activities (Armitage et al., 2014) 2-10 Figure 2-6: WDM Strategies (Armitage et al., 2014) 2-12 Figure 2-7: Domestic water use (CoCT, 2012) 2-14 Figure 3-1: Gatesville and Surrey Estate 3-1 Figure 3-2: Distribution of demand types 3-2 Figure 3-3: Annual Outdoor demand 3-3 Figure 3-4: Catchment and Cape Town WO 3-5 Figure 3-5: Components of domestic water use (Fisher-Jeffes, 2014) 3-6 Figure 3-6: Calibrated evaporation rates 3-9 Figure 3-7: Calibrated Residential outdoor AADD 3-10 Figure 3-8: WED Savings 3-14 Figure 4-1: Water Demand Breakdown 4-1 Figure 4-2: Demand met v/s costing 4-3 Figure 4-3: Water savings over different adoption rates 4-4 Figure 4-4: Comparison between GWH and RWH 4-5 Figure 4-5: Water saved over different adoption rates 4-6 Figure 4-6: Medium savings 4-7 Figure 4-7: High savings 4-7 Figure 4-8: New demand with WED scenarios 4-8 Figure 4-9: Comparison of savings with adoption rates between RWH and GWH 4-9 Figure 4-10: Comparison between different measures 4-10 Figure 4-11: Demand met for garden only 4-12 Figure 4-12: Differences in WED savings 4-13 Figure 4-13: Cost v/s demand met of Scenarios 22 to List of Figures

11 X Figure 4-14: Maximum percentage of savings for each measure 4-17 Figure 4-15: Cost versus Demand met 4-20 Figure 4-16: Cost v/s average percentage savings 4-21 Figure 4-17: Optimum tank sizes used for each city 4-22 Figure 4-18: Water tariffs trends with cost of scenarios for Cape Town 4-25 Figure 4-19: Water tariffs trends with cost of scenarios for ethekwini 4-26 List of Figures

12 XI List of acronyms AADD BFN CoCT CSIR CT DBN DWA ECSA EL ESD ET GIS GWH IF IPCC JHB NDP PE PTA PMB REUM RSA RWH SPG SWMM SuDs TWD URSHM = Average annual daily demand = Bloemfontein = City of Cape Town = Council for Scientific and Industrial Research = Cape Town = Durban = Department of Water Affairs = Engineering Council of South Africa = East London = Ecologically Sustainable Development = Evapotranspiration rates = Geographic Information System = Greywater Harvesting = Irrigation factor = Intergovernmental Panel on Climate Change = Johannesburg = National Development Plan = Port Elizabeth = Pretoria = Pietermaritzburg = Residential End- Use Model = Republic of South Africa = Rainwater Harvesting = Springs = Storm Water Management Model = Sustainable Drainage Systems = Total Water Demand = Urban Rainwater/Stormwater Harvesting Model List of acronyms

13 XII WDM WED WM WSC WSS WSUD YAS YBS = Water Demand Management = Water Efficient Devices = Washing Machine = Water Sensitive Cities = Water Sensitive Settlement = Water Sensitive Urban Design = Yield After Spill = Yield Before Spill List of acronyms

14 Introduction Background to study Water scarcity is one of the most pressing issues experienced worldwide. Water resources are being fully exploited and some countries will feel its effects sooner than others, if not already (Rijsberman, 2006). This challenge will be further aggravated by the growing impacts of climate change, economic growth and development. In view of this, a new concept, Water Sensitive Urban Design (WSUD), was developed to help remedy this matter by aiming at modifying the conventional urban water cycle throughout the design, planning and management stages. WSUD was conceived for developed countries and has already been applied worldwide. South Africa is a water scarce country and development has been hindered due to water related issues (RSA, 2011a). However, RSA s situation does not fully allow the implementation of these WSUD measures directly as do developed countries Problem statement The concept of WSUD has as goal to achieve Water Sensitive Cities (WSC) and its framework suits the need of mostly developed countries. Developing countries such as South Africa face more pressing issues and have other priorities which are not accounted for in the initial WSC ideology. The implementation of these concepts in RSA therefore necessitated further studies leading to Water Sensitive Settlements (WSS) which is more appropriate for the current conditions of the country. It is still, nonetheless, unclear of how this is applicable in a real catchment in RSA and how the idea should be best presented to concerned parties. There are several WSUD measures fulfilling the ultimate aim of the concept which can be applied to urban catchments. The main concern about the application of these measures is the efficiency of the systems and more precisely the extent to which these are economically feasible to be socially accepted. The different variables linked to effectiveness of the measures have to be further analysed by applying them to different extents to existing catchments. 1.3 Aim and objectives The objectives of this research project are to further discuss and clarify how WSS can be achieved on a small catchment, to advise the City of Cape Town on how to proceed to redevelop the city and convince the stakeholders of its application through a case study done on two small catchments, of approximately 1.5 km 2. Surrey Estate and Gatesville, Cape Town have been identified for the purpose of this research. Four possible WSUD measures were identified to study the effect of their respective and combined implementation in the catchment, aiming at decreasing the latter s dependence on potable water. These are: Chapter 1: Introduction

15 1-2 Rainwater Harvesting (RWH); Greywater Harvesting (GWH); The use of high and medium savings water efficient devices(wed); and On-site leakage management. The results were used to assess their impacts on the total water balance of the area and the economic viability of investing in such methods to decrease the existing stress on potable water supplies. These were then compared to similar catchments in the eight municipalities of the South African Cities Network (SACN). 1.4 Scope & limitations of research project The amount of data available during the time of study was not enough to obtain accurate enough water demand data for the eight other municipalities. It was assumed that the calculated AADD for Gatesville and Surrey Estate, Cape Town, will be the same as for the other cities. This was done to obtain an idea of how effective the measures are countrywide. Another major assumption made was on the calculation of the water demands per property due to the limited amount of information available on the households in the catchment. The uncertainties associated with these values were attempted to be minimised but further detailed studies should be done to get more accurate values. The scope of this research is limited to an overview of the possible water savings and their respective implementation costs that could be obtained more thoroughly in Cape Town but more generally in the other eight cities considered. Chapter 1: Introduction

16 Literature Review 2.1 Water scarcity in South Africa Water is an integral part of hydrological systems. Globally water resources are being exploited and depleted to meet the needs of mankind. Most countries have enough water resources to supply their population and sustain the right balance of flows to protect the environment. The real issue, however, is to keep this balance despite the growing challenges such as climate change, urbanisation and the need development (Barilla Group et al., 2009) and Africa in particular has been identified as being particularly vulnerable to the changing climate and the effect of urbanisation due to its envisaged low adaptive capacity and vulnerability (AfDB, 2007). South Africa receives a mean annual precipitation of 490 mm p.a, classifying it as a water scarce country (Rijsberman, 2006). This is approximately half of that of the world and is further restricted by high infiltration rates, allowing a small 8.6% of the rainfall to be available as surface runoff. Rainfall in South Africa is unevenly distributed across the country and occurs mainly away from urban areas (WWF-SA, 2013). According to the WWF-SA, almost 98% of South African reliable surface water resources are already being exploited. The current South African water supply capacity is approximately 15 billion m 3 but this is severely constraint by factors such as irregular rainfall and limited underground aquifers (Barilla Group et al., 2009). The country is be further affected by these conditions compounded with the effects of unequal distribution of services brought on by Apartheid. This latter entailed significant backlogs in service delivery, that is, 12 % of the population still do not have access to safe water supply (DWA, 2011) South African water usage The water allocation in South Africa is as shown in Table 2-1. Table 2-1: Water allocation in SA (DWA, 2011) Sector Estimated Percentage Agriculture 60 Urban 27 Industrial 3.5 Afforestation 3 Mining 2.5 Power generation 2 Rural 4 Chapter 2: Literature Review

17 2-2 The agricultural sector accounts for most of the water supply demand but is not expected to increase substantially in the coming years. The urban sector, including domestic water use which is projected to increase considerably with rapid urbanisation (DWA, 2011). The focus of the study will therefore be on urban water usage and management Conventional urban water cycle The issue of water scarcity in South Africa does not only originate from prevailing climatic conditions. Current water systems are based on a conventional urban water cycle. It consists of a linear structure. Water from reticulation systems is only used for its end purposes and returned to watercourses while stormwater is collected and discharged to watercourses. Similarly, wastewater is collected in sewage systems, treated and again discharged directly into watercourses (Armitage et al., 2014). The conventional approach focusses on providing systems capable of collecting and removing stormwater as soon as possible without any treatment while wastewater is treated and released to water bodies. This usually results in polluted waterways degrading the natural environment, reducing infiltration and production of large amount of poor quality runoff (Wong & Eadie, 2000). Figure 2-1 shows the differences between the typical conventional urban cycle and the natural water cycle. Figure 2-1: Natural &Urban water balances (Hoban & Wong, 2006) Chapter 2: Literature Review

18 Current and future challenges As mentioned before, almost 12% of the population does not have access to safe water supplies as a legacy of Apartheid. This is due to segregate spatial planning schemes resulting in inequality in services distribution system (Turok, 1993). The provision of adequate water to all RSA citizens is one of the most urging issues in the country (Armitage et al., 2014). South Africa currently has a population of around 52 million but population growth projections estimate that this number will increase to 53 million by 2025 (DWA, 2011). As a result, the domestic water demand is expected to increase to as high as 35 % by 2025 without addressing the current water supply backlogs. Resolving these backlogs will increase the total domestic water usage by 200 million m 3 per annum, that is, 6 % of the current national water use (DWA, 2011). Coupled with the effect of urbanisation and development as people migrate into cities with access to higher level of services, the total national water demand is expected to increase to 17.7 billion m 3 by This exceeds the current water supplies by almost 17% and adds additional pressure to the already stressed water resources (Barilla Group et al., 2009). This situation will be further aggravated by the effect of climate change. Studies have shown that water supply capacities will decrease due to reductions in precipitations or as evaporation increases (New, 2002). Global warming is expected to in turn increase the water demand by 0.6% per year by 2020 mainly in the agricultural sector which solely accounts for 60% of water withdrawals (New, 2002; DWA, 2011). This will be caused by increased variation in the frequency and intensity of rainfall, decreases in soil moisture and increase in evapotranspiration (IPCC, 2008). On average, climate change will also widen the gap between supply and demand by an estimated 30% (Barilla Group et al., 2009). South African water ecosystems are threatened by increased levels of pollution with poorly treated wastewater, untreated stormwater, agriculture fertilisers and mining by-products. This lowers water quality of available water resources, resulting in 60 % of river ecosystems being endangered and 25 % being critically endangered. This is mainly due to inefficient uses of water resources including high level of water wastage and an inadequate water management (DWA, 2013). Despite the fact that South Africa is a water-scarce country, it does have adequate resources to meet its short to medium term requirements. This can be achieved by ensuring the viability of the sector by exploiting new potential resources and promoting sustainable water delivery, management and governance (DWA, 2012) These facts raise concerns about the conventional urban cycles and how water resources are being managed and urge to find remedial actions to empower urban water cycles to cope with the mentioned concerns. Chapter 2: Literature Review

19 2.2 Water Sensitive Urban Design With the development of the idea of water conservation, several strategies have been analysed to make the urban water management more viable. Water Sensitive Urban Design (WSUD) is a recent concept, having been introduced in the early 1990s and has been applied in countries such as Australia, New Zealand, US and Japan. It is, however, a relatively new notion in South Africa although there has been sustainable urban drainage measures applied in some metropolitan areas. Its application is still being discussed and modified to suit the needs of the country. WSUD integrates the design of all four streams of urban water cycle, that is, water supply, wastewater, stormwater and groundwater management with urban design and environmental protection (BMT WBM Pty, 2009; Wong & Brown, 2008). It requires a major socio-technical change from conventional approaches of designing, planning and managing developments. WSUD introduces the idea of water sensitivity into urban design and ensures that it is given due prominence in the design of urban areas to ensure the protection of aquatic environments while providing water services. It includes the concept of sustainability into development by promoting better lifestyles and infrastructures without depleting resources or degrading the environment (Wong, 2006). It has the potential to act as a relief on South African water sources and deter any move towards energy intensive solutions such as desalination plants. It has also been described as being a possible means of connecting the divided settlements in RSA while remedying to water scarcity issues while promoting equity in the provision of services. The sustainability and resilience of water cycles are also improved by empowering the systems to adapt themselves and resolve to alternative sources of water and better water management schemes. This concept is a combination of system based technologies and new philosophies of urban design, planning and management with respect to sustainability (Armitage et al., 2014). The goal of WSUD is to manage all streams of water as a resource having quantitative and qualitative impacts on land, water and biodiversity, and the community s aesthetic and recreational enjoyment of waterways. This encourages the adoption of Ecologically Sustainable Development (ESD). It aims at mainly: (BMT WBM Pty, 2009; Mildura Rural City Council, 2005) Efficiently managing potable water through demand and supply managements by considering alternative sources of water and use of water efficient appliances; Treating and recycling of wastewater and stormwater while decreasing the volume of wastewater produced and improving the quality of water released to the environment; 2-4 Keeping an adequate balance of receiving waterways and natural hydrological systems; Improving the aesthetic value of developments and encouraging communities to adopt these measures; Chapter 2: Literature Review

20 2-5 Allowing a certain degree of resilience in those developments by decreasing its dependency on potable water and their impact on the environment; and Adding a long-term value to development while minimising costs. The WSUD framework changes the conventional urban water cycle to a cyclical resource efficient one where water resources are used more than once, reflecting the natural water cycle. Figure 2-2 shows the transition from linear to cyclical urban water management. Figure 2-2: Mirroring natural water cycle (Hoban & Wong, 2006) WSC, WSS and the transitional framework The ultimate goal of the WSUD is to help cities move towards becoming Water Sensitive Cities (WSC) through more sustainable water management. Brown et al. (2008) describes six stages along the path with modifications towards more sustainable futures forming a continuum until the city achieves its objectives. The concept of WSC was initially conceived in developed countries such as Australia and doesn t take into account several conditions unique to developing countries. In the case of South Africa, several issues were identified with realising the concept of WSC. The most prevalent one is the backlogs in service delivery across the country as stated before. Most of the South African urban areas can be considered as having reached the Drained City stage in Figure 2-3 but the rest of South African settlements haven t even reached the first stage. This Chapter 2: Literature Review

21 2-6 disparity is not accounted for in the WSC concept since RSA is already facing challenges for all its settlements to reach the first stage. It will be tricky for the government to promote the ideologies of WSUD wholly without addressing concerns about equity. Social acceptance, which is not present in the WSC context, is the key to the proper implementation of WSUD principles but the framework above does not involve solving difficulties such as these. Figure 2-3: Transition to WSC (Brown et al., 2008) Water sensitivity was also found to be contextual to the concerned country. Water Sensitive Settlements (WSS) is therefore a concept which is adapted for the RSA where the design, management and planning of the water cycle is incorporated with the principles of WSUD to achieve ecologically sustainable development using blue-green infrastructure. Green Infrastructure was initially associated to energy crises for production of renewable energy. This notion has been modified to implicate sustainable development and the protection of the environment. Blue-green infrastructure consists of ensuring the sustainability of the ecosystems through all physical organisational and social structures by linking it to blue corridors, that is, networks of water bodies.(brown et al., 2008; Armitage et al., 2014). Achieving the objectives set by the WSS concept is based on a series of iterative processes linking three fields to guide and transform the current system into a more sustainable one. It consists of Water Sensitive Urban Design, Water Sensitive Urban Planning and Water Sensitive Urban Management and is illustrated by the South African Framework for achieving Chapter 2: Literature Review

22 2-7 the same goals as WSC (Armitage et al., 2014). This framework takes into account the two extreme types of settlements and level of development of the country. In the context of South Africa, economic growth must be directed towards an equitable distribution of benefits amongst the people and not just promoting environmental sensitivity for water services to be sustainable (Carden, 2012). The formal settlements illustrated in Figure 2-4 have already been developed as drained cities and can be compared to Australian or European cities. These areas can follow the path by already introducing water sensitive concepts into their planning by reconstructing or redeveloping them while educating the inhabitants on the benefits of water sensitive systems. Meanwhile, informal settlements can be upgraded to proper water supply cities with basic water services and once these concepts have been applied and tested on formal cities, the informal settlements can in turn apply the most effective ones. This is mostly restraint due to financial issues since the budget allocated for the upgrade of informal settlements allow mostly for only basic service provision. Greenfield development on the other hand should be done with water sensitive concepts from the very beginning(armitage et al., 2014). Figure 2-4: WSS Framework (Armitage et al., 2014) Chapter 2: Literature Review

23 Stakeholder involvement To create acceptance of WSUD measures in South Africa, it is crucial to present the benefits of adopting these to each type of stakeholder in the society. Each one has different expectations and priorities and the benefits of these measures do satisfy them to some extent. Table 2-2 shows some examples of how WSUD measures should be presented to each stakeholder. Table 2-2: Area of interests for stakeholders (Armitage et al., 2014) Stakeholder Politicians City Officials Private developers Community interest groups Environmental interest groups Private individuals Area of interest / Opportunities Provision of basic services; job creation Costs and ease of maintenance Increased profit/public image Job creation; public health and safety Protection of the environment Additional costs/ benefits per household Challenges for the South African context Several plans and strategies have been put in place by the Government, committing itself to assist authorities to manage the impacts of urbanisation and avoid a water crisis. The National Development Plan (NDP) and National Water Resource Strategy 2 aim at eliminating inequality and developing better water management schemes by placing water as a priority; both working towards achieving these goals by 2030 (RSA, 2011; DWA, 2013). The NWRS-2 proposes seven themes all with respect with water sensitivity but is not backed up with enough scientific support for innovative solutions (Armitage et al., 2014). The main challenge with the South African WSS framework and other attempts at promoting sustainable development is the constraints that the Municipalities have to deal with, both financial and ethical. Municipalities cannot make only ecosystem sustainability their priority while people still do not have access to their basic human rights. Developments leading to WSS must be done with medium and long term goals in mind. Municipalities also have the power to encourage the inhabitants of formal settlements to take water sensitive actions on their own by enforcing relevant policies and legislations. This would allow them to focus their resources on other issues. Advancements in the upgrade of settlements have been very slow and the government has proven to act mainly under the pressure of non-governmental organisations, as responses to civil unrest and natural disasters (Armitage et al., 2014). RSA also has backlogs within its institutions. The concept of WSS requires cooperation between the different providers of services but a silo mentality exists in the country s Chapter 2: Literature Review

24 2-9 institutions. WSUD integrates planning, design and management stages but these three aspects of the urban water cycle are controlled by different departments with minimum coordination between themselves. Another major issue lies with the capacity and skills required in the local authorities as compared to those in developed countries (Carden & Armitage., 2012). The lack of knowledge on the actual benefits of WSUD in South Africa, hinders its application mainly due to social issues concerning health and safety. These uncertainties were mainly found while developing the idea of wastewater reclamation schemes and introducing purified wastewater as safe potable water. The main issue with implementing these measures is therefore more social and institutional and must be addressed to develop these strategies to their full potential (Armitage et al., 2014). The importance, concepts and benefits of WSS also have to be simplified and explained for inhabitants to better understand them. The potential benefits of implementing such strategies include poverty alleviation, strengthening the democracy and ecological conservation (Carden & Armitage, 2012). To be able to properly apply these strategies, the capacity of RSA must be improved by developing new policies, educating people and developing the necessary tools which none of the above mentioned documents discuss Benefits of WSUD Implementation of WSUD can provide social, environmental and economic benefits simultaneously. These include savings in potable water by promoting the use of recycled water as alternative water sources for non-potable uses, decrease in volumes of contaminated water discharged into watercourses while ensuring economic growth (Armitage et al., 2014). South Africa has already resolved to use desalination plant as a means of alternative water source but is highly energy intensive having a significant carbon footprint (Shrestha et al., 2011). WSUD principles make use of methods that have as minimum toll on the environment as possible to use. Environmental benefits such as protection of groundwater resources and the quality of water resources can be achieved with better stormwater management and urban development. Improvement in stormwater drainage systems will decrease the risks of flooding and the volume discharged into water courses. This can be reduced by re-using stormwater as a source of water supply (Wong & Eadie, 2000). Resilience of cities and settlements adopting these practices is developed enabling them to withstand future water and climatic challenges. They are more apt to absorb disturbances in their water cycles and still be functional. They also self-modify to cater for new circumstances while allowing for freedom to increase capacity for learning and adaptation for development (Wong & Brown, 2008). More ecosystem goods and services such as provision of food, prevention of soil erosion, water purification and even climatic regulations can be provided with the WSUD approach. It allows ecosystems to revert to their natural courses and provide an Chapter 2: Literature Review

25 2-10 essential support for the regulations and maintenance of ecological processes and life support systems (Groot et al., 2002; Armitage et al., 2014) Overview of WSUD strategies WSUD combines the idea of water sensitivity with urban planning and design by combining all the aspects of the water cycle. There are several types of infrastructural changes with respect to ESD, which can be embedded in the design of urban water systems. The flowchart in Figure 2-5 gives an overview of the different WSUD activities. WSUD activities are broken down into two main parts; urban water infrastructures and design and planning. An urban water infrastructure deals with all infrastructural needs of an ecologically adequate environment without overlooking human needs. The design and planning part in turn looks at the water cycle taking into account the needs of the community and environment by analysing the benefits and effectiveness of the activities. Figure 2-5: WSUD activities (Armitage et al., 2014) The four main components of urban water management are further explained below: (Armitage et al., 2014; Armitage & Fisher-Jeffes, 2012) Chapter 2: Literature Review

26 2-11 i) Stormwater management measures take a Sustainable Drainage Systems (SuDS) approach. SuDS modify the conventional drainage practices with respect to sustainable development by mirroring the natural hydrological cycles. They aim at improving the effectiveness of stormwater runoff quantity and quality management while preserving the ecological aspect and enhancing the amenities and biodiversity. SuDs options vary from good housekeeping, source controls, and local controls to regional controls depending on the scale of application. ii) iii) iv) Sanitation/Wastewater minimisation builds on the concept of fit for purpose approach of WSUD. It involves the recycling of wastewater generated which is usually discarded, thus decreasing the extent to which watercourses are contaminated by these effluents. It leads to a smaller flow of wastewater in sewerage systems and the performance of the WWTP also improves with less wastewater requiring treatment. Recycled wastewater can be further used for non-potable purposes as an alternative water source, increasing the efficiency of the urban water cycle. In line with WSUD objectives, issues of sanitation provision and options to the urban poor are also considered to ensure the wellbeing of both the environment, community and the economy. However, the sustainability of these sanitation systems does not depend on whether or not these meet their critical objective, which is the health objective. There are several sanitation options available such as dry and wet sanitation options. The wet option, is a water intensive one, consisting of pour flush toilets, aqua privy, septic tanks and conventional, simplified, settled and vacuum sewerage. The dry option is more water saving in form of VIP, composting and bucket toilets, vault/vacuum tanker. The dry option, despite having the most water savings while fulfilling the basic objective of sanitation, is again faced with the social acceptance issue. The design and implementation of sustainable sanitation systems must consider the effective use of resources while finding a compromise between community expectations and their sustainability. WSUD measures take all the components of the urban water cycle into consideration including groundwater. Groundwater management is the component which receives the least attention but is regarded as a valuable resource with 80% of surface water resources being fully exploited in RSA. The protection of groundwater quality and recharge can be greatly influenced by WSUD principles. Sustainable water supply involves the modification of the water balance by increasing the efficiency of both supply and demand sides with the help of sustainable water management strategies. It is derived from the principles of Water Conservation (WC), which deals with efficient use of water, minimising losses and protection of water resources, and Water Demand Management (WDM) which refers to practices leading to more efficient and sustainable use of water resources (Deverill, 2001). Chapter 2: Literature Review

27 Potable water saving schemes Water scarcity in South Africa can be mitigated with sustainable water management strategies making efficient use of available water resources. These consist of the cyclical urban water management and modification of the conventional one by reducing potable water requirements, minimising wastewater generation and promoting alternative water sources. Water Conservation and Water Demand Management strategies tackle both the supply and demand sides of the cycle. South Africa is already almost fully exploiting its water resources and therefore, WC and WDM targets at balancing the water demand with the existing water supplies while covering all quantity, quality and time space dimensions of water use. WC focusses on the principles of ESD while WDM deals with the operational side of demand management of the whole urban water cycle including issues on supply-side management. There are four categories of strategies which are used to optimise efficient water use. These are the structural, operational, economic and socio-political methods dealing with a range of factors ranging from physical infrastructures, technologies, operational strategies, cost recovery and laws and regulations. WDM strategies are further classified into smaller categories as illustrated in Figure 2-6. Figure 2-6: WDM Strategies (Armitage et al., 2014) Chapter 2: Literature Review

28 2-13 The following sections will focus on managing water losses, water efficient devices and alternative water sources Water losses- leakages In Africa an average of 39 % of water is lost through the distribution systems. More leakages and pipe bursting occur as the infrastructure ages, therefore increasing the level of water wastage. The reduction of losses from leaks can be achieved by several programs and are divided into two categories; proactive and passive leakage controls (CoCT, 2007). The proactive programme consists of mainly pressure reduction through installation of pressure valves and the formation of reticulation leak detection teams. Most of pipe bursts have been noted to have occurred at night. Reticulation systems are designed so that they can provide a minimum acceptable pressure at any time but due to the fact that water demand is higher during the day than at night, pipes tend to burst due to this pressure differences. This can be controlled by establishing District Metered Areas (DMAs) which consist of divided parts of the network. These DMAs then monitor the flow through the meters and identify areas where installation of pressure reducing valves is necessary. On-going maintenance programmes have to be scheduled to ensure proper maintenance of these valves. The reticulation leak detection teams in turn tend to any situations in which high levels of water are unaccounted for without being responsible for any repairs. These are done by the operational and maintenance staff of the particular areas. The other category consists of preventive maintenance, passive leakage control which deals with reported leaks and the development of a uniform Operation and Maintenance policy (CoCT, 2007). On-site leakages in turn contributes significantly to the water demand by properties as read by the meters and usually occur at low flow rates on the consumer s property. This kind of loss is categorised into authorised consumption and includes leakages from household appliances and fittings. In RSA, the site leakage rates vary between low to high income properties varying between 20 to 60l/h/property. A study carried out in low, medium and high income areas in RSA showed that the poorer areas tend to have higher percentages of properties with on-site leaks as compared to high income ones. The cities of Cape Town, Johannesburg and Maungang have been investigated to obtain the occurrences of leakages in different areas and their leakage rates. In Johannesburg, it was estimated that only 70% of the water delivered to property accounted for the actual use and the rest was lost through on site and apparent losses (Couvelis & Van Zyl, 2012; Lugoma, van Zyl, & Llemobade, 2012) Water efficient devices Water efficient devices are those which improve water use efficiently with minimum wastage without any reduction in performance. There are numerous options available to reduce domestic and commercial water consumption via both the consumers and utilities. Water Chapter 2: Literature Review

29 2-14 conservation using water efficient devices makes use of structural, operational, economic and socio-political methods (Still et al., 2008). In the domestic setting, household water end-uses generally involve indoor and outdoor activities such as gardening, toilet flushing, bathing and washing. A study undertaken by the City of Cape Town shows how most of the potable water supplied is used in a household and is illustrated in Figure 2-7. All of the end uses with the exception of cooking and gardening involve the use of appliances which can be more water efficient. 62 % of the water demand can therefore be decreased by the introduction of indoor water efficient devices. The gardening component can also be decreased with the use of drip systems but will not be investigated in this study. 13% 20% 35% 3% 29% Gardening Toilet flushing Cooking Bathing Cleaning Figure 2-7: Domestic water use (CoCT, 2012) A typical shower normally takes up approximately 59 litres per event while up to 114 l/event is used up for using washing machines (Haarhoff, 2006). This represents a considerable amount of wastage of potable water. The use of water efficient devices such as metering and low flush toilet has proven to have a major impact on the reduction of water wastage. In a study carried out by Still (2008) to analyse the efficiency of water efficient devices at the household level, it was found that households actually save on costs while decreasing their demand. For example, an average saving per toilet flush to a less efficient one is 5 litres and with the use of several devices simultaneously, up to 25% reduction per capita per day demand can be achieved. It was also found that consumers would be more disposed to using water efficient devices if increasing public awareness and the information about water that they can possibly save is properly communicated to them. There are several factors preventing people from using these devices, for instance, some people did not see the need for them or were not aware of them. However, several measures can be taken to persuade people to resort to these devices including water restrictions, increase in price of water or rebates on installation of these devices. The City of Windhoek is one example where the implementation of demand Chapter 2: Literature Review

30 2-15 management strategies including the use of water efficient devices, allowed their consumption to decrease by almost 30% (Still et al., 2008) Alternative water sources The need to find alternative sources of water in the WDM strategy is mostly motivated by the fact that settlements use water resources which are not necessarily obtained over their own catchment areas. One of the key pillars toward achieving sustainability is the need to diversify water sources and treating the settlements as catchment areas by introducing a greater variety of infrastructures (Wong & Brown, 2008). Alternative water resources in form of harvested or recycled water are already present in the catchments and must be treated as valuable resources to decrease their dependencies on potable water. Collected and recycled water can be used for some of domestic end-uses which do not need good quality potable water. This strategy will help on the supply side of the balance by decreasing the demand of potable water (Armitage et al., 2014) Rainwater harvesting Rainwater harvesting is generally described as the collection and storage of water runoffs from roofs on which rain has directly fallen on (Pacey & Cullis, 1986).The use of rainwater has long been in use in some countries. Treated harvested rainwater usage can be considered a viable solution to water shortages by reducing drinking water consumption and decreasing the flows in stormwater systems. In turn, the inflow of pollutants in to rivers are mitigated due to reduced flows in stormwater systems (Nolde, 2007). The collected water can be used again for fit for purpose solutions such as toilet flushing and gardening (Armitage & Fisher-Jeffes, 2012). Rainwater harvesting consists of run offs roofs in catchments while stormwater harvesting include run offs from all surfaces, that is, roads, ground and pavements. This section will also limit itself to the study of rainwater harvesting in residential areas which is a more realistic option in an already developed catchment. There are several options concerning the collection and storage for harvesting rainwater and stormwater, these include:(armitage et al., 2014) i) Tank Storage; ii) iii) Open Storage; and Managed Aquifer Recharge Tank storage is mostly used for rainwater harvesting for a small catchment while open storage, such as dams, ponds and lakes, and managed aquifer recharge are mostly used for stormwater. Rainwater tanks are typically used to collect runoff from roofs. These are readily available in South Africa and can be properly maintained with screens to control mosquitoes and vector Chapter 2: Literature Review

31 2-16 proliferations. The collection of runoff will decrease the volume of water discharged into rivers and can attenuate flood peaks. The development of settlements decreases the porosity of grounds and causes water to flow without being retained as it was before any development. The collection of rainwater off these properties roofs imitate the natural behaviour of grounds before development as less water is allowed to flow off properties. There are several considerations while choosing this particular option including budgetary constraints, rainfall intensities, space availability, impervious catchment areas, potential rainwater uses and the ecological water reserves. However, the water quality might be compromised and should be used only for non-potable water end uses. It is relatively expensive to be applied for houses and may be ineffective during hot and dry seasons. Households should also be educated about the potential risks of harvested water, that is, its health risks and necessary maintenance precautions (Armitage & Fisher-Jeffes, 2012). Rainwater harvesting schemes have already been applied in other countries. Australia, for example, has invested in a water sensitive urban redevelopment making use of rainwater tanks, infiltration trenches and a central basin. The collected water was planned to be used for domestic purposes including hot water, toilet flushing and open space irrigation. The quality of the rainwater stored in the tanks complied with the Australian Drinking Water Guidelines even though it has a higher composition in metal and chemical pollutants. The combination of hotwater system and water treatment processes such as flocculation and settlement were sufficient to obtain water suitable for drinking. Water savings up to 45 % is expected with the use of rainwater for hot water systems and toilet flushing but may rise to 60 % if rainwater is also used for irrigation purposes (Coombes et al., 2000) Greywater recycling Wastewater can be divided into two components; blackwater consisting of water contaminated with faecal matter and urine and greywater, water released from other domestic activities such as water from baths, showers and washing machines. Blackwater is extremely contaminated and dangerous for human contact. Its treatment is complex and therefore, expensive for recycling. The conventional sewage system combines greywater and blackwater and is transported in the same pipe systems. Greywater accounts for almost 75% of the combined residential sewage but only light greywater, that is, water not including kitchen effluents have low organic contents (Hansen & Kjellerup, 1994). It is less contaminated than blackwater and can be used for domestic activities such as toilet flushing and irrigation which are currently using potable water (Eriksson et al., 2002). Recycling of greywater for domestic use will need additional infrastructure such as pumps, tanks and disposal systems with the co-operation of residents to ensure proper functioning of the network. There are issues with the storage of greywater since the latter s quality will be further degraded due to chemicals and micro-organisms present in it. This adds Chapter 2: Literature Review

32 2-17 to the difficulty of implementing such measures and the community needs to be actively involved (Eriksson et al., 2002) Dual reticulation systems The possibility of having dual reticulation systems for areas close to wastewater treatment plants may be a cost effective solution and again tallies with fit for purpose principle of WSUD. The City of Cape Town has considered this option as one of the most feasible alternative to surface water resources but the extent to which this can be exploited is unknown due to the lack of measurement equipment and control functions (CoCT, 2007). Reclaiming wastewater reduces the flow in networks and the volumes of discharge into waterways. Wastewater is treated in wastewater treatment plants before being released back to the environment. This water is still contaminated with significant nutrient and pollutant levels and has harmful effects on the receiving water bodies; furthermore most of South African WWTPs do not conform to quality standards and have damaging effects of the waterways (Bhagwan, 2013). Treated wastewater can be an economically viable option if properly implemented as it decreases the load on potable water supplies for activities not requiring potable water. The introduction of treated greywater and wastewater back in the water reticulation systems through secondary pipes will undoubtedly incite resistance from the public specially if they are not properly sensitised about the matter. It will be worsened by the actual situation in South Africa, created by unequal distribution of services triggered during the apartheid. Communities have expectations of appropriate reticulation systems for everyone and any slight modifications from their idea of conventional reticulation systems can receive opposition. Communities must be educated of the benefits and maintenance of such systems for them to be accepted. Sanitation systems are subjected to simple designs but must be robust to achieve its aims as being a sustainable system (Armitage et al., 2014). There is an urgency to provide proper sanitation systems in informal settlements since it restricts South Africa s ability to provide full sustainable waterborne sanitation systems to other developed settlements as shown in Figure 2-4. Before its application, several challenges must be resolved including wastewater re-use complexity, social acceptance and health and environmental quality criteria (Armitage et al., 2014) 2.4 Modelling the benefits The various benefits and outcomes of applying water saving strategies can be assessed using modelling tools. The effects of implementation of these measures in South Africa can therefore be predicted instead of just relying on case studies. There are numerous models on the market and each varies depending on its variables and functions. The two types of models used in the study are stormwater models and water cycle models. There are others which deal with urban groundwater modelling but is not relevant to the content of the research. Chapter 2: Literature Review

33 2-18 Stormwater models include the Model for Urban Stormwater Improvement Conceptualisation (MUSIC), the Source Loading and Management Model (SLAMM) and the Storm Water Management Model (SWMM). MUSIC was first developed to deal with stormwater hydrology and pollution impacts by modelling downstream flow control and water quality benefits for Best Management Practices (BMP) for water pollution control. The model combines treatment measures helping in the planning and designing phases by producing stormwater quality performances. The objective of SLAMM is to predict the flow and pollutant concentrations in stormwater discharges by calculating the mass balances of each component in the water. Its main aim is to link urban water run off to water quality. SWMM in turn has several possible outputs. The model can calculate the volume of runoff, its pollutant level and the simulation of its path through pipes, channels, storage and treatment devices (Armitage et al., 2014). SWMM can also generate climate data SWMM using rainfall and temperatures. The cost of each these models vary but SWMM 5.1 is available for free downloads unlike MUSIC and SLAMM (Fisher- Jeffes, 2014). Urban Volume and Quality (UVQ), Urban Developer and Water Evaluation and Planning system (WEAP) are a few of the models available for urban cycle modelling. UVQ determines the impact of development on the total water cycle and assesses the different approaches to the provision of water, stormwater and wastewater services to a wide range of land use types. The main drawbacks of the model is that it assumes that the whole model has the same climate since it can only use one climate file and doesn t consider economic analysis (Mitchell & Diaper,2005; Armitage et al., 2014). Urban Developer is considered as an up to date model which analyses the water cycle holistically dealing with water supplies, stormwater and wastewater systems with the ability to assess new measures such as water efficient devices, alternative water supplies and recycling. Daily demands from end uses can be modelled using daily or smaller time steps and at a range of levels. The model isn t, however, available for free use. WEAP in turn models the water balance of municipal, agricultural and complex river systems and is based on GIS. WSUD measures can also be modelled using WEAP dealing with water conservation, pollution tracking, power generation and the project s benefit-cost analysis (Armitage et al., 2014). Chapter 2: Literature Review

34 3. Methodology This section will outline the steps and methods that were used during the course of the study. Surrey Estate and Gatesville, found Athlone as shown in Figure 3-1, have been identified as the catchment consisting of mainly middle income residential areas. The objective of the research is to examine the potentials of implementing rainwater and greywater harvesting systems, water efficient devices and minimising leakages on the catchment s total water balance. These four measures were chosen due to their suitability to a residential region having adequate scope for their applications. The results will later be used to compare the application of the same measures in different areas in South Africa. 3-1 Figure 3-1: Gatesville and Surrey Estate Chapter 3: Methodology

35 3.1 Data Collection Land Classification Using the Geographic Information Systems (GIS), the different land uses of the catchment were depicted by the use of polygons. The land area was classified into categories, that is, roofs, roads, gardens and school grounds to estimate the areas allocated to each erf. Each erf was allocated specific roof, garden and impervious surface areas. This is done to estimate the household counts, amount of run off on these surfaces and the potential indoor and outdoor demands generated from these. The area was further categorised as domestic, educational, industrial or institutional zones. The nature of the demands generated from each of these categories differs from each other depending on each category s use and therefore the demand calculation steps and parameters are different. Figure 3-2 illustrates the distribution of the different categories in the catchment. 3-2 Figure 3-2: Distribution of demand types Chapter 3: Methodology

36 Outdoor demand (kl) 3-3 There are 5 schools, 1 hospital in both suburbs and about 30% of the area is occupied by commercial and industrial spaces. These however, consisted of small scale businesses varying from restaurants to bus washing services Calculation of capita per household Monthly billing records for each property in Gatesville and Surrey Estate from May 2010 to April 2011 were obtained from the City of Cape Town and used as an input to calculate an approximate number of people per dwelling. It was assumed that during winter months, that is, May, June and July, the billing data only reflected the indoor demand for residential areas, with no outdoor demand contributing to it. Rainfall and evaporation rates were used to calculate the outdoor demand in the area and it was found that during May, June and July there was no need for irrigation and this is described in Figure 3-3. Negative outdoor demands were obtained during the calculations showing that the plants had negative moisture deficits, that is, they obtained their required water from rainfall. This will be further explained in Section Figure 3-3: Annual Outdoor demand The billing records were cleaned to exclude unusual data, such as excessive meter readings due to pipe bursts, faulty meters and leakages. Properties with billing data less than 6 kl and greater than 350 kl were also excluded. As a result, only about 60 % of the properties had adequate records to be used for household counts calculations. The Indoor Demand Calculation model (Fisher-Jeffes, 2014) uses each end-uses frequency and volumes as well as their individual Chapter 3: Methodology

37 3-4 contribution to the total water demand to calculate the approximate number of individuals living in a particular property. The South African government carried out a population census recording demographic, economic and social data countrywide in 2011 called Census Population counts for Gatesville and Surrey Estate were obtained from Statistics South Africa s website. The households having capita/hh varying between 1 and 10+ was grouped together for each suburb as shown in Table 3-1. Table 3-1: Household counts Number of people/hh Gatesville Surrey Estate Total The other 40% of the properties were allocated a random household count, to match the overall trends given by Census The overall proportion of houses having specific number of people was kept to the ones in Table 3-1 as much as possible Climate data Daily rainfall and temperature data from 2000 to 2014 were obtained from Weather SA. The data collected was from the Cape Town International Airport station (Station A3) which is located closest to the designated area (within 7 km) as shown in Figure 3-4. It was assumed that there will be uniform rainfall and evaporation rates over the catchment due to its small area which would be under the influence of the same climatic conditions. The only closest meteorological centre near the area is the Cape Town WO. The rainfall and evaporation data from 2003 to 2012 were used to be able to get an idea of how the climatic conditions in RSA vary over the past years. Chapter 3: Methodology

38 3-5 Airport Catchment Figure 3-4: Catchment and Cape Town WO The minimum and maximum temperature records were used as an input on Stormwater Management Model (SWMM 5.1) to obtain daily evaporation rates using Hargreaves method. Both rainfall and evaporation rates are necessary for the calculation of outdoor water demands and as inputs for the rainwater harvesting models. This will be further elaborated in Section The application of these methods on similar catchments in the main South African cities required specific rainfall, temperature and evaporation rates data for these areas. These were provided by Weather SA and from the DWAF website. 3.2 Water demand calculation Depending on the land use type, the annual average daily demand (AADD) for each erf was calculated. For residential areas, this is done using Jacobs & Haarhoff (2004) Residential End- Use Model, (REUM), by estimating the frequency and water demand using nodes such as taps, showers, baths and gardens. The final water consumption value is obtained by multiplying the values by the number of people using each end-use daily. The other land use type areas water demand were estimated from the Guidelines for human settlement planning and design (CSIR, 2000) which provides values of demand ratio for basic water demands for these land use types. The outdoor water demands were estimated again using the REUM model accounting for both various vegetation types and swimming pools. Water demand for vegetation depends on the moisture levels which in turn depend on the evapotranspiration and rainfall of the area. Chapter 3: Methodology

39 Residential Indoor demand Gatesville and Surrey Estate consist of middle income residential areas. The residential indoor water demands are mainly made up of water needed for end uses such as toilets, showers, baths and washing machines which combined, use the most significant amount of water in households. The Indoor Demand Calculation model was provided by Lloyd Fisher-Jeffes, which used the calculated number of people per household and the winter months billing data to obtain an approximate indoor demand per erf. Figure 3-3 showed that gardens didn t need any irrigation during May, June and July, meaning that the water demand reflected by the billing data for these months only accounted for indoor water demand. The model calculates an average daily consumption per capita of the suburb based on population counts obtained from Census 2011 and the cleaned billing data available. For 60 % of the properties which had appropriate billing data, the indoor AADD for these properties were considered to be the same as the average of the winter months billing data which were cleaned of over readings caused by leakages. The indoor demand was assumed to remain constant throughout the year for these properties. A major assumption was made by supposing that for the other nine months, the indoor demand will be the one based on the winter months and the difference between the billing data and the indoor demand can automatically be accounted by the outdoor demand. The capita/hh for these properties were then calculated using the average billing data for winter months and the average consumption per capita for each property calculated before. The remaining 40 % of the properties with unusual winter months data or missing data were allocated random house counts to fit the proportions of the house counts obtained from Census 2011 shown in Table 3-1. Their indoor AADD were based on summarised main indoor end use factors, that is, showers, toilets and washing machines contributing to indoor water demands. Figure 3-5 shows the percentage of each end-use that was assumed to be contributing to the final demand. 21% 26% 29% 24% Toilets Washing Machine Showers/Bath Gardens Figure 3-5: Components of domestic water use (Fisher-Jeffes, 2014) Chapter 3: Methodology

40 3-7 The total AADD per erf for these properties were based on multiplying the demand per end use by the number of people in a household and summing the volume obtained for all the end uses. AA per end use per capita volume used for each event frequency (3-1) Total AA per erf AA per end-use per capita household si e (3-2) The remaining AADD from their billing data were assumed to form part of their outdoor demand. The results involving indoor AADD have major uncertainties originating from 40 % of the data which are based on random numbers. This uncertainty is mainly dealt with in calibration process for the outdoor demand Outdoor demand The outdoor demand estimate was again done using the REUM model which depended on vegetation types and garden areas. Swimming pools were also accounted for but only a small proportion of households had them, contributing to their respective property s billing data. Pools will not be considered as an end use suitable for RWH systems since less than 5 % of the residential properties have them and would not have a noticeable impact on the water demands and potential savings. Vegetation water demand was calculated using the rainfall data, vegetation types and garden areas of each property. Gatesville and Surrey Estate mainly consisted of lawns and initial crop factors given in Jacobs & Haarhoffs (2004) were used to calculate the water demand. Daily rainfall data and evaporation rates were available for the study period and therefore, daily outdoor water demands were calculated based on those. The daily outdoor water demand is calculated using the irrigation factors (IF), crop factor (k), evaporation rates (p), effective rainfall (r), the average number of days in a month (D) and the ground surface area (SA). The equation above describes the relationship linking these variables and gives the demand as l/day. A I SA (k p -r (3-3) The water demand is given by its moisture deficit, ET-r, where ET is the evapotranspiration rates and r is the effective rainfall. The effective rainfall in turn depends on R which is the average rainfall and the equation 3-4 was used to determine its value. Chapter 3: Methodology

41 3-8 R (R 2 mm r [(0. 0 R 12. (2 R (R 1 2 ] (3-4) ET represents the amount of water required by the cropped surface and is in turn obtained by T k p (3-5) The surfaces were initially assumed to consist of lawns and therefore corresponding crop factors were taken from Jacobs & Harhoffs (2004). The same equation was used to calculate the demand for swimming pools which made use of monthly pool cover factors (f), evaporation factors (k), and pool surface areas (s). The total outdoor demands were added to the indoor demands to obtain the total demands. 3.3 Calibration of calculated values The calculated evaporation rates and AADD values were adjusted using different variables or factors to match measured billing data Evaporation rates vaporation rates couldn t be obtained for the specific period of study since DWAF only recorded these from 1957 to However, using SWMM 5.1 with minimum and maximum daily temperatures from 2003 to 2012, approximate daily evaporation rates were calculated. The values obtained from DWAF were A pan factors. These values had to be cleaned to remove uncertainties and errors in readings caused by overflowing or the influence of heavy rainfall on the pans leading to high daily evaporation without necessarily causing any overflows. The numbers were therefore scaled using Symonds tank to reservoir evaporation factors which are given in Table.3-2. The factors represented in Table 3-2 are average monthly factors and were assumed that they remain constant throughout the months. Table 3-2: Monthly Pan factors (Fisher- Jeffes, 2014) Month Factor Month Factor Month Factor Month Factor January 0.84 April 0.88 July 0.83 October 0.81 February 0.88 May 0.87 August 0.81 November 0.82 March 0.88 June 0.85 September 0.81 December 0.83 Chapter 3: Methodology

42 Evaporation rates (mm) 3-9 The scaled daily evaporation rates from 1957 to 1977 were calculated and compared to those from 2003 to Monthly adjustment factors were calculated by comparing the monthly evaporation rates from 1957 to 1977 to the ones from 2003 to Adjustment factor measured evaporation rate calculated evaporation rate (3-6) The initial daily evaporation rates obtained from SWMM were then multiplied by their respective monthly adjustment factors, obtaining values closer to the measured ones for 2003 to Figure 3-6 shows the difference between the scaled values from 1957 to 1977 and the calculated ones from SWMM 5.1. The adjustment factors adapt the calculated numbers to match the measured ones Months SWMM values DWAF Adjusted Figure 3-6: Calibrated evaporation rates Residential AADD The total outdoor and indoor demand included the households which did not have enough data to obtain reliable house counts, causing the total demand to exceed the measured values obtained from the billing data. There was only one year s billing data available for Gatesville and Surrey Estate and it was assumed that the water demand of the properties will stay the Chapter 3: Methodology

43 AADD (kl) 3-10 same during the period of study, that is, from 2003 to The water demand of the properties depends on several factors and the climatic conditions of each year. This was a major assumption to make but an average monthly consumption of all the ten years studied was used to minimise the effects of this issue. The winter months billing data were assumed to consist of only indoor AADD and matched the calculated indoor demand. The use of random generation of demands for 40 % of the properties added to the disparity between the measured and calculated water demand values. As a result, only 60 % of the properties which had reliable water demand values were used to calibrate the water demands. The indoor demand values were based on the winter months assumption and stayed constant throughout the year. Hence, only outdoor demands were modified during summer months to fit the data obtained from the billing data by changing the crop factors while keeping effective irrigation as 1. The crop factors carried major uncertainties since the crop type of the area was only roughly estimated and varied from property to property. The calculated outdoor AADD were changed so that the total AADD matched the ones from the billing data as shown in Figure Months Adjusted AADD Calculated AADD Measured AADD Figure 3-7: Calibrated Residential outdoor AADD Chapter 3: Methodology

44 3.4 URSHM 3-11 For the purpose of this research, the models used will be required to simulate the effects of grey water re use, rainwater harvesting, water efficient devices and provide scenarios where several strategies are run simultaneously. The models used take into account factors such as surface areas, infiltration, annual rainfall, evaporation as well. There are several models available for rainwater harvesting systems having different functions while using the same inputs. They are based on water mass balances given by calculating the volume present in the tank after the demand was met. The following equation describes the relationship (Ward et al., 2010). Where, V t : Volume of water stored at the end of a particular time interval t; Q t : Inflow during t; and Y t : Yield during t. t t-1 t t (3-7) The models vary using YAS, Yield After Spill, or YBS, Yield Before Spill, methods which controls the amount of supply, demand and overflow needed for the storage volume needed. YAS was found to be more relevant for rainwater and stormwater systems while YBS is used mostly for dam modelling (Fewkes & Butler, 2000). The Urban Rainwater/Stormwater Harvesting model (URSHM) was developed by Lloyd Fisher-Jeffes and uses the same principle described above to calculate the volume collected based on roof and surface run offs. The model can be run on a daily time steps and stores the water left over after yielding for a flexible time period. It also analyses ten different systems based on several percentages of water retained from the runoff and the system adoption rate of a catchment. There are four outputs set for four objectives depending on the intended results of the research, the primary objective being the volumetric reliability of the system, that is, the percentage of the demand met by the system. The other three objectives are to find objectives fitting the following requirements (Fisher- Jeffes, 2014): the minimum cost per kl of collected water; maximising volumetric reliability while keeping the cost of implementation less than the cost of water supplied; and balancing cost of harvested water and the volumetric reliability. The model also calculates the optimum tank size for the calculated volume of water to be stored and used. However, the tank size depends on the garden area available for the tank to be stored. Underground rainwater tanks are too expensive to implement and maintain and will not be further discussed in this study. The costs per kl of the water saved are also calculated while Chapter 3: Methodology

45 3-12 taking into account discount and interest rates. The implementation, operation and maintenance costs are computed and since there is no monetary benefit derived from the system, the benefits are represented in terms of water saved over different period of time. The same model can be modified to analyse the effects of greywater harvesting systems. The model calculates the volume of rainfall collected over a day based on daily rainfall data and adds it back to the system. The input can be changed to add a percentage of the wastewater flow generated from households back to the supply side instead of using rainfall as input. The same outputs, that is, volumetric reliability, demand met, optimum tank sizing and costs per kl can be obtained. 3.5 Water Demand Management (WDM) models As was pointed out in the literature review, the project will only consider leakage management, water efficient devices and alternative water sources as WDM strategies that are applicable in the particular catchment Rainwater Harvesting The suitability of implementing rainwater harvesting schemes in the catchment was investigated using the Urban Rainwater Stormwater Harvesting Model (URSHM V06) developed by Lloyd Fisher-Jeffes. URSHM Version 6 uses evaporation rates, rainfall data, garden and roof areas, household counts and their respective AADDs. The model uses the surface areas and climate data to work out the total runoff volumes off the roof of each property and calculates the amount captured in rainwater tanks. Water losses through depression storage by roof surfaces are also accounted for. Different tank sizes, costing components and end use demands are analysed to obtain the demand met, volumetric reliability and costs of each tank size. The tank sizes analysed ranged from 0.25 kl to 30 kl catering for different end uses for which rainwater could be used. The model calculates the daily runoff captured in each of the rainwater tank sizes daily over ten years for each property. The volume stored in the tank is used for the targeted end uses and the remaining is stored for a period of 30 days. The remaining water contributes to the total volume of water collected the next day and the process goes on. The volumetric reliability of each tank is therefore calculated using the following equation. Where Yield olumetric reliability yield demand = the available water collected dispensed for use, (3-8) Demand = the daily demand of non-potable water for rainwater for particular end- Uses Chapter 3: Methodology

46 3-13 The optimum volumetric reliability, which is the highest percentage of demand met, was set as the target. Consequently, for each property, the scenario and tank size yielding the best volumetric reliability was chosen as being the best alternative Greywater Harvesting The potentials of greywater harvesting in Gatesville and Surrey Estate were investigated using the same model as for rainwater harvesting, that is, URSHM. The inputs were changed and instead of using rainfall as an input to the system, light greywater was added back to the system. Light greywater represented water generated from the bathroom basins, showers and washing machines. This was done by applying a percentage of the AADD to the input. Not all components of greywater can be recycled as these can cause potential health hazards and cannot be stored. The volume of greywater generated in one day was assumed to be completely used up or discarded after 24 hours. 70% of the greywater was assumed to be suitable for recycling and the retention period was set to one day. The model worked out the demand met on a daily basis for ten years for each property using the same principles as for rainwater harvesting. Recycled greywater cannot be used for human consumption and contact between humans and the water must be kept to a minimum. The end uses for which greywater harvesting were investigated but were kept to only garden irrigation and toilet flushing. The model was modified accordingly to satisfy demands generated from these specific end uses. The output also uses volumetric reliability as the main aim of the analysis and the same range of tank sizes are studied to find the optimum one for each property Water Efficient Devices (WED) The main components of the household demand, that is, baths, bath basin, dishwashers, kitchen sinks, showers, toilets and washing machines were modelled for high and medium savings and compared to the standard devices. Figure 3-8 compares the volumes used by standard devices with high and medium savings devices. The model for calculating this option was provided by Lloyd Fisher- Jeffes. Chapter 3: Methodology

47 Volume (l) Bath Basin Dishwasher Kitchen Sink Shower Normal Toilet Washing Machine Standard Device Medium Savings High Savings Figure 3-8: WED Savings The probability that all households will implement the measures, at the same time is negligible. Therefore several scenarios with different proportion of the household adopting either medium or high savings devices were analysed. Table 3-4 explains the different scenarios with their respective adoption rates. Table 3-3: WED scenarios Scenario Current Medium Low The model was run 1000 times with the different scenarios. Each household was given a random number which indicated the type of devices they were using (standard, high or Chapter 3: Methodology

48 3-15 medium) and for each scenario, every property was allocated a corresponding new water demand. The new total demand for each scenario was then added using all the properties. It was also assumed that if a household is investing in one of medium or high savings end use, they will invest in all the end uses to get consequent savings On-site leakage management Couvelis (2012), studied the proportion of households in different suburbs in Cape Town which have on-site leaks. There were no studies done in Gatesville or Surrey Estate in particular and therefore, areas examined in the study, which were similar to the concerned catchment, were used. It was assumed that the percentage of leakages will be the same as Observatory and Thornton. It was based on the fact that both Observatory and Thornton have similar income levels and similar suburb characteristics such as type of dwellings as Gatesville and Surrey Estate. According to Couvelis (2012), the leakage rates and occurrences depend most significantly on income levels. Table 3-4 summarises the leakage rates in these suburbs. The Indoor Demand Calculation model removed a leakage factor from the billing data before any calculations were done. Keeping the same principles as the WED Calculator model, the properties were allocated a random number. Those with a number below , that it less than % of the properties, will have leakages with a flow of 21.2 l/h/property. The volume per day lost in those particular properties is then added to their respective initial AADD. Table 3-4: Leakage rates and occurrences Leakage rates (l/h) Suburb % leaks minimum mean maximum Observatory Thornton Gatesville/ Surrey Estate The total volume of water lost in all properties was calculated and added to the AADD calculated earlier. It was assumed that all leakages were fixed for the purpose of this study since the savings due to leakage management was found to be relatively small compared to the ones from the other measures. Scenarios involving different percentages of leaks fixed would not make a significant difference to the overall results. Couvelis (2012) also included leakage flows and occurrences in other areas such as Mangaung and Johannesburg in the same report. The above steps were repeated to obtain the amount of water lost due to leakages in those areas. However, there were no data for leakages for the other areas investigated and therefore, it was assumed that these percentages will remain fairly constant throughout the country. Chapter 3: Methodology

49 Scenarios The WDM measures were combined in a number of ways to obtain the possible savings from these. Each measure was initially investigated using specific end-uses in a household calculating the demand met for each of them individually. These were then combined together. Rainwater harvesting and greywater harvesting were directly investigated using URSHM while combinations of these measures with the use of water efficient devices affected the output of both rainwater and greywater harvesting. Leakages were already removed from the calculated AADD in the initial calculations and therefore for each examined area, only a percentage was applied to the total water consumption depending on the availability of the data. The different scenarios investigated were chosen to study the effect of demand on the feasibility and effectiveness of each method and their combinations. Table 3-7 explains all 29 scenarios considered in this research. In case of RWH systems, the only indoor end uses considered were showers, toilets and washing machines as they are the main users of water in households and only gardens as outdoor end use. As explained earlier, pools are scarcely present in the region and will not affect the results. As for GWH systems, its indoor end-use is only for toilets while outdoor end use is again gardens. It was assumed that that all households converted to the use of either high savings WED or medium savings WED to obtain the optimum amount of water saved. In case only a few of the intended end uses in each category are used, they are specified in their respective cells. ALL represents all the mentioned end-uses in each category. The combined scenarios represent all the measures highlighted in the same row that would be implemented at the same time. The highlighted cells describe the allocated end-uses for each particular measure. For instance, Scenario 20 indicates the use of RWH systems for all indoor end uses (shower, washing machines and toilets) combined with the use of medium savings WED and GWH systems for gardening. Leakage management only represents a percentage added to the initial calculated AADD and therefore no end-use was allocated to it. Chapter 3: Methodology

50 3-17 Table 3-5: Scenarios Scenarios RWH GWH WED Leakages indoor outdoor indoor outdoor High Medium 1 ALL garden 2 garden 3 Toilets only 4 WM only 5 Toilets/showers 6 WM/showers 7 WM garden 8 Toilet/showers garden 9 garden 10 Toilet only garden 11 ALL 12 ALL 13 ALL ALL 14 ALL ALL 15 garden ALL 16 garden ALL 17 garden ALL 18 garden ALL 19 ALL garden ALL 20 ALL garden ALL ALL 23 garden 24 ALL 25 ALL 26 garden ALL 27 garden ALL 28 ALL garden ALL 29 ALL ALL ALL Chapter 3: Methodology

51 3.7 Applicability of concept to other South African areas 3-18 The models were run again for cities in the eight metro municipalities in South Africa obtained from the South African Cities Network s website 201. These are: 1. Buffalo City; 2. Ekurhaleni; 3. ethekwini; 4. Johannesburg; 5. Maungang; 6. Msunduzi; 7. Nelson Mandela Metropole; and 8. City of Tshwane. Rainfall and evaporation rates for each of these cities were used as inputs for the models used for Cape Town. However, the same household counts and billing data used for Gatesville and Surrey Estate were used along with the inputs due to the lack of billing data in those areas. This causes a great deal of uncertainty since winter months in other areas may not consist of only indoor AA which was calculated based on Gatesville and Surrey state s billing data. The same indoor demand was used for each city but the URSHM calculated each property s outdoor demand using their respective climate data.this study will only investigate the potentials of the WSUD measures generally in these other municipalities. Data from cities representing each of these municipalities were obtained from Weather SA. Due to restrictions in the amount of data acquired, the following cities were chosen to represent them. Table 3-6: Major municipalities and associated station number Municipality City Station Number Mangaung Bloemfontein B0 Buffalo City East London B8 Nelson Mandela Metropole Port Elizabeth B1 City of Tshwane Pretoria Ekurhaleni Springs A3 Msunduzi Pietermaritzburg ethekwini Durban A2 Johannesburg Johannesburg Chapter 3: Methodology

52 Results This section deals with the analysis of the results obtained from the different modelling processes described in Chapter 3. These results are used to model the water balance of the catchment by considering the current water demand and the different outputs possible. The section ends with a comparison between the individual measures and their combinations, with a final water balance. 4.1 Catchment water usage The modelling of these measures used mostly data for Gatesville and Surrey Estate in Cape Town for the calculation of each property s water demand. The billing data from May 2010 till April 2011 were used for these purposes and the total water demand from the catchment came up to Ml/yr for both Gatesville and Surrey Estate. The domestic water demand made up for approximately 75 % of the total water demand given that the catchment is mainly a residential one. The other components of the total water demand are illustrated in Figure 4-1. Each category, that is, commercial, hospital and schools demands were calculated using their monthly billing data for the given period and compared to the total amount of water used. Commercial 17% Hospital 6% School 2% Residential 75% Figure 4-1: Water Demand Breakdown Chapter 4: Results

53 4-2 The study focussed mainly on the residential application of the four measures mentioned due to the diverse type of commercial buildings in the area such as factories and bus wash services. The demand from hospitals and schools were also investigated but there were some missing data for the schools monthly water consumption in the billing data. The main focus of the study remained the residential areas. It was found that most of the properties had gardens and 5% of them had swimming pools and the outdoor demand for water accounted for almost 27% of the domestic demand. This can be explained by the fact that most of properties have small garden areas and some have none. Nonetheless, pools were not used as a potential end use for rainwater harvesting since only a small percentage of the properties have them. The calculated data for Gatesville and Surrey Estate was assumed to be the same for similar catchment in terms in other cities due to a lack of time and information. 4.2 Cape Town Gatesville and Surrey Estate, Cape Town s annual rainfall average is very close to South Africa s average annual rainfall and receives most of its rain during the winter months. Cape Town climate system is classified as a subtropical climate characterised by hot and dry summer months (November till April) and cool and wet winters (May to October). This affects the moisture content and evaporation rates which tend to be quite high in these conditions. These affect the outdoor demand and the effectiveness of both rainwater harvesting and greywater harvesting which depends mostly on climatic conditions and the outdoor demand Rainwater harvesting (RWH) As mentioned above, the average rainfall of 498 mm for Gatesville and Surrey Estate was assumed to be constant throughout the catchment and is the same as the Cape Town International Airport. The different scenarios concerning rainwater harvesting measures were modelled and Table 4-1 summarises the results. The maximum savings using only rainwater harvesting were made when the demand was greatest, that is, all indoor end-uses (showers, washing machines and toilet flushing) and gardening were assumed to use collected rainwater. This was represented by Scenario 1. The efficiency of the system depends on the demand allocated to each scenario. The optimum tank size is then chosen by comparing the different costs and volumetric reliability of each tank. Chapter 4: Results

54 Costs (R/kl) 4-3 Table 4-1: RWH Scenarios Scenarios Description Demand met (Ml) Overall reduction in demand % Optimum Tank size (kl) Costs(R/kl) 1 RWH(indoor+outdoor) RWH(outdoor) RWH(toilet) RWH(WM) RWH(toilet+ showers) RWH(WM+ shower) RWH(garden +WM) RWH(garden+ toilet +showers) The model analyses different systems having different volumes of run off collected and compares it to the cost per kl of the harvested water. However, the objective of the model was set to choose the system giving the highest volumetric reliability. The volumetric reliability represents the percentage of demand met by the system. The cost per kl of water saved decreases as the demand for rainwater in the household increases, that is, more end-uses are to use the collected water. This gives an idea of the economic viability of the system Demand met (Ml) Figure 4-2: Demand met v/s costing Chapter 4: Results

55 Savings (Ml/year) 4-4 The success of applying RWH systems in households was investigated through different adoption rates in the catchment. This consisted of varying the percentage of households adopting RWH systems in increments of 10%. Figure 4-3 shows how the low, medium and high savings scenarios work out with increasing adoption rates. It shows that the difference between minimum and maximum savings is quite minimal indicating that the different runoff parameters do not have as much effect on the volume collected as do increasing adoption rates Min Median Max adoption rates Figure 4-3: Water savings over different adoption rates Greywater harvesting (GWH) The input for the greywater system was assumed to be 70% of the AADD, that is, 70% of the wastewater produced by the households will be added back to supply side. However, despite the reliability of greywater supplies, only two end uses have been investigated for this measure. This is due to the risks associated to using greywater which contains contaminants potentially dangerous to human health if not handled properly. The results obtained from the models showed a significant increase in demand met and decrease in the resultant costs compared to the same end use demands being met by rainwater harvesting systems. Table 4-3 compares the results of modelling the same end uses using RWH and GWH. The overall reduction in demand for gardening purposes was found to be 6.6 % more with GWH systems than RWH systems with a significant decrease in costs from R 197/ kl to R40.6/ kl. Chapter 4: Results

56 4-5 Table 4-2: GWH Scenarios Scenarios Description Demand met (Ml) Overall reduction in demand % Optimum Tank size (kl) Costs(R/kl ) 2 RWH (garden) RWH (toilet) GWH (garden) GWH (toilet+garden) Greywater harvesting is more reliable than rainwater harvesting since its input is generated by the households themselves and do not depend on external factors. Therefore, the volumetric reliability of both GWH scenarios is higher than those in Scenarios 1 to 8. The optimum tank size obtained depends on the volume collected. However, greywater will only be stored in tanks for a day and therefore the tank sizes are smaller than the ones used in RWH, that is, 1 kl tanks as compared to the 5 kl tanks needed for RWH. Again, while comparing the two GWH scenarios investigated, the demand met for GWH for garden and toilet flushing is much higher than the garden only scenario leading to a slight decrease in its costs Demand met(ml) Overall reduction in demand % Optimum Tank size (Kl) Costs(R ) RWH(outdoor) RWH(toilet) GWH( garden) GWH(toilet+garden) Figure 4-4: Comparison between GWH and RWH Chapter 4: Results

57 Water saved (Ml) 4-6 The cost of implementing and maintaining GWH systems is less than half of that of RWH as illustrated in Figure 4-4. This is explained by the absence of treatment for greywater as treatment and prolonged storage of greywater causes an increase in the cost per kl to up to R 300/kl. The viability of GWH system was also determined using several adoption rates with maximum, median and minimum savings as shown in Figure Min Median Max Adoption rates Figure 4-5: Water saved over different adoption rates Water Efficient Devices Different scenarios involving the percentage of the current population switching to the use of medium and high savings water efficient devices were investigated. These included the use of the following end uses. The savings ratio for each end use is given in Table 4-3. Table 4-3: Savings for high and medium ratios End Use High Ratio Medium Ratio Bath Basin Dishwasher Kitchen Sink Shower Normal Toilet Washing Machine Domestic Ratio Chapter 4: Results

58 4-7 The maximum savings possible using the high ratio will lead to a decreased demand which can go as low as 42 % of the initial demand while with medium ratio, the demand can decrease to 59 % of the initial one. It was assumed that the households switching to WED will do so for all their devices to get optimum savings. New demand 59% Water Saved 41% Figure 4-6: Medium savings New demand 42% Water Saved 58% Figure 4-7: High savings The scenarios describing the percentage of properties keeping their current appliances and adopting medium and high savings WED were discussed in Section and the models gave water savings ranging from 38 Ml/ year to 184 Ml/year and the tendency is shown in Figure 4-8. Chapter 4: Results

59 New demand (Ml) Scenario 1 Scenario 2 Scenario 3 Scenario 4 Scenario 5 Figure 4-8: New demand with WED scenarios Leakage Management The total annual residential AADD, Ml, determined in Chapter 4, was multiplied by to estimate the AADD with leakages which came up to be Ml. The calculated value had already been cleared of leakages in the Indoor Demand Calculator model. The water saved by resolving on site leakages came up to 3.1 Ml/year which represents an annual saving of 0.8 % of the total water supply Comparing the four measures The four measures discussed in the previous sections depicted each measure s individual contribution to increasing the efficiency of water usage in the catchment. This section will compare the extent of each measures contribution to water savings. The effectiveness of RWH systems depend on climate which is a variable that cannot be controlled and the water savings by these systems are completely dependent on climatic conditions. Figure 4-7 compares the water savings against adoption rates of both GWH and RWH systems. GWH having a more reliable source of input, produces much better results than RWH. Even with adoption rates as low as 10%, GWH system has twice as much savings as RWH systems at 10 % adoption rates. It should also be noted that the maximum savings for RWH were obtained with Scenario 1 which involved both all indoor and outdoor end uses while the maximum savings with GWH system was only modelled for toilet flushing and gardening purposes which is Scenario 10. Despite Scenario 1 having a greater demand for Chapter 4: Results

60 Water saved (Ml) 4-9 RWH than Scenario 10, the demand met by the GWH system is much higher than the RWH system RWH GWH adoption rates Figure 4-9: Comparison of savings with adoption rates between RWH and GWH The fact that Scenario 10 had a smaller demand than Scenario 1 shows that the GWH system can cater for more demand. The quality of water used in GWH system, nonetheless, restricts the extent to which it could be applied.. Greywater use for toilet flushing can pose health issues if incorrectly handled. Figures 4-5 and 4-9 used this particular scenario to show how effective GWH systems can be but greywater use for toilet flushing will not be used in the combination scenarios. The individual contribution of each intervention in the new water balances is compared in Figure 4-8. Leakage management yielded the lowest saving of 3.0 Ml/year followed by RWH systems, WED and GWH systems. Each systems saving were based on a 100% adoption rate and were assumed to be working in perfect conditions. The GWH system described in Figure 4-10 caters for both toilets and gardening purposes. Chapter 4: Results

61 Water saved (Ml/year) RWH GWH WED Leakage management Figure 4-10: Comparison between different measures The application of these measures will surely decrease the overall water demand of the catchment but will be faced with financial issues. The costs of installing and maintaining RWH and GWH systems are quite consequent. GWH systems in particular need considerate care and property owners must be informed of its functioning and risks. The extent of use of GWH systems can be increased but the costs of treatment for the prolonged storage of greywater is consequent and therefore, is beyond the scope of this research Combinations A significant increase in water savings was noticed when the above measures were combined into several scenarios including leakage management and Table 4-4 summarises the results obtained from modelling scenarios. The total demand for RWH scenarios, however, decreases since the volume required by the targeted end uses also decreases. This is due to the introduction of WED which decreases the water demand of the household appliances. The demand met by combining High savings WED and RWH for indoor end uses, comes up to Ml while the one combining Medium savings WED and RWH for indoor use gives a slightly higher demand met. This can be explained by the fact that a higher demand per scenario is required from the RWH system using medium water savings devices which require more water compared to high saving devices. Chapter 4: Results

62 4-11 Table 4-4: Combination Scenarios Cape Town Scenarios Description Demand for particular end uses (Ml) Demand met(ml) Reduction in total demand % Optimum Tank size (kl) Costs(R/kl) 13 High WED + RWH(indoor) Medium WED+ RWH(indoor) High WED + RWH(garden) Medium WED + RWH(garden) High WED + GWH (garden) Medium WED+ GWH(garden) WED high+ RWH(indoor)+GWH(garden) WED medium+ RWH(indoor)+GWH(garden) , , Leakage+ RWH Leakage+GWH(garden) Leakage+ WED high Leakage +WED medium Leakage +WED high+ GWH(garden) Leakage +WED medium +GWH(garden) Leakage+ WED high+ RWH(indoor)+GWH(garden) Leakage +WED medium+ RWH(indoor)+GWH(garden) , , The combination of GWH and WED systems also decreases the viability of the GWH systems. The application of WED significantly decreases the flow of wastewater from the targeted end Chapter 4: Results

63 Water saved(ml/year) 4-12 uses and consequently the volume of water recycled from the flow. The outdoor demand met decreased from 42.5 Ml/year to Ml/year for a combination of high savings WED and GWH for gardens. Figure 4-11 gives the differences in demand met for gardening purposes only without taking into account the water saved from the use of WED GWH( garden) High WED + GWH (garden) Medium WED+ GWH(garden) Figure 4-11: Demand met for garden only The cost per kl of the GWH system in turn increased while an overall saving of up to 33.7% of total water demand was still achieved. The effect of changing the volume of outflow from the end-uses can be seen with Scenario 18 in which Medium Savings WED and GWH for gardens are combined. The demand met for garden is much higher than that of using high savings WED while the overall reduction in demand is still less than the latter since the amount of water saved using high savings WED is more significantly more. The use of greywater was restricted to gardening in the combined scenarios with RWH systems providing for indoor demands. Leakage management was added to the combinations and the highest savings percentage came out to be almost 47.2 % of the current demand. Leakage management contributed for 0.8 Ml in the final volume saved. It was also noticed that despite the use of high WED which decreases the flow of greywater, a higher demand met (125.6 Ml) for GWH systems for gardens was achieved than the use of high savings WED and RWH system for gardens (110.8 Ml). It shows that even though WED decreases the efficiency of GWH systems, GWH systems can still ensure a more reliable supply of non-potable water than RWH systems. Chapter 4: Results

64 Water saved(ml/year) 4-13 The gap between high savings and medium savings WED when applied individually is 26.2 Ml but this number decreases as these are combined with other measures. The effectiveness of the merged systems takes into account the combined effects of the measures on each other. Scenario 28 depicting all the measures with the use of high savings WED has a total saving of Ml while Scenario 29 with the same measures but with the use of medium savings WED has a total demand met of Ml. The difference between the two measures came up to be about 14.5 Ml which is almost 45% less than the initial gap. The cost of implementing either scenario comes up to be almost the same. These differences are shown in Figure The effectiveness of any combination cannot therefore be judged by the individual contribution of each measure Combined Combined Individual WED high savings Individual WED medium savings Figure 4-12: Differences in WED savings Scenarios 26 to 29, nonetheless, are unrealistic since they combine a perfect functioning of all four systems. These scenarios include the use of two separate tanks for RWH and GWH systems on each property. The costs to operate and maintain such systems were estimated as being substantial and could probably not be applied in all households in the catchment, given the its income level. A further breakdown of the cost of Scenarios 22 to 29 is shown in Figure The fluctuations in the trend can be explained by the differences in implementation and treatment costs of each measure. Chapter 4: Results