UTILISING RAINWATER FOR NON-POTABLE DOMESTIC USES AND REDUCING PEAK URBAN RUNOFF IN MALAYSIA

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1 UTILISING RAINWATER FOR NON-POTABLE DOMESTIC USES AND REDUCING PEAK URBAN RUNOFF IN MALAYSIA AHMAD JAMALLUDDIN BIN SHAABAN National Hydraulics Research Institute of Malaysia (NAHRIM) Km 7 Jalan Ampang Kuala Lumpur Malaysia ahmadj@mail.moa.my ADHITYAN APPAN HYFLUX (S) Pte Ltd 40 Changi South Street 1 Singapore cappan@ntu.edu.sg ABSTRACT Rapid socio-economic development has begun to put a strain on Malaysia s water supply and drainage facilities. This strain came to the fore on the back of the 1998 drought induced water shortages which brought unpleasant water supply disruptions for 1.8 million residents in the Klang and Langat Valley. This drought event jolted the nation to explore alternative water resources such as rainwater for conserving the public water supply. Similarly rapid urbanisation which brought an increase of impervious areas and reduction of natural storages has increased urban peak runoff, burdening city drainage systems and compounding city flash flood problems. Consequently, NAHRIM embarked on a study on rainwater harvesting and utilisation system (for non-potable household use), coupled with detention storage (to reduce peak storm runoff), for a double storey terrace house at Taman Wangsa Melawati, Kuala Lumpur. The rainwater system comprises of gutters, downpipes, first flush storage, rainwater cum detention storage tank, a pump, a roof tank and separate distribution pipes. The rainfall and runoff from the roof are measured and the non-potable water use of the house occupants is also metered. Sizing of the storage tank is done taking into consideration reliability of the delivered water, roof catchment area and space constraints in the house compound. The economic aspect of the system such as unit cost of rainwater is also determined. The rainwater quality in the storage tanks are compared with the piped public water, WHO Drinking Water Guideline and the Interim National River Water Quality Standard. The new Urban Stormwater Management Manual developed by the Department of Irrigation and Drainage (DID) is referred to in the design of the detention storage. The effect of the rainwater cum detention storage system when extended to every house in the housing area with regard to peak runoff reduction for a selected design storm is also investigated.

2 1. INTRODUCTION Annually water resources in Peninsular Malaysia originating from rainfall is abundant at 2470 mm or 324 billion m 3 compared to 10.8 billion m 3 per annum consumed for domestic, industry and agriculture purposes. Even then, water supply disruptions due to a tight water supply demand situation aggravated by a lack of rainfall over catchment areas coupled with river pollution problems at the water intakes do occur, as in the 1998 drought which brought unpleasant water supply disruptions for some 1.8 million Klang and Langat Valley residents. This drought spurred Government interest in rainwater harvesting and utilization. On 7 May 1998 the Minister of Housing and Local Government expressed the Government s interest for houses to be designed for collecting rainwater. In 1999, the Ministry of Housing and Local Government produced a Guideline on Installing a Rainwater Collection and Utilization System. In support of the current interest in rainwater harvesting NAHRIM, through collaboration with other government agencies and universities, embarked on R&D regarding rainwater utilization (for domestic, office and mosque complex, industry and agriculture use) and runoff reduction. This paper is focused on a current study carried out by NAHRIM for a double storey terrace house located at Taman Wangsa Melawati, Kuala Lumpur (Figure 1) on utilising rainwater for non-potable household use and also reducing peak storm runoff. 2. RAINWATER SYSTEM The rooftop has cement tiles and has a roof area of 60 m 2. The rainwater is conveyed from the rooftop to the storage tanks via PVC gutters and pipes. Rainwater from the rooftop is usually contaminated with dirt, bird droppings, leaves, etc. The first flush of rainwater from the roof surface is directed into the first flush tank of 200 litres to filter out these materials from the rainwater before it is stored in the ground floor storage tanks. For the 1 st phase of the study, two black High Density Polyethylene (HDPE) tanks with a 2500 liter capacity each were installed as storage tanks. The water use and quality are monitored over one year. In the 2 nd phase, these two black HDPE tanks are replaced with a better storage tank design taking into consideration the aesthetic and utility aspects. It is a brick storage tank of 5000 litres capacity and the space above the tank is used as a

3 children s play area and also for drying clothes (See Figures 2a, 2b and 2c) litres of storage is allocated for rainwater reuse (bottom portion), while 1700 litres is for detention storage (top portion). A 1.0 horsepower electric pump with minimum head of 12 m was installed to pump water from the ground storage tank to the roof rainwater tank. This tank was installed on the roof in addition to the existing potable water roof tank that is a mandatory requirement. The additional tank has a separate rainwater supply for nonpotable household use. The study house also has a separate plumbing system to cater for the rainwater usage. Since rainwater was to be used for non-potable use, the plumbing system was installed in such a way that there was a bypass connection for each flushing cistern. In case of water shortage or non-availability of rainwater, the public water supply can be switched on. The rainwater plumbing system was also connected to the washing machine pipe and pipe for general cleaning. 3.0 WATER USE AND SIMULATION MODEL The house under study has two adults and four school going children. The house has three bathrooms. The amount of rainwater used for facilities was monitored manually installing mechanical water meters in each facility. Readings were taken and recorded manually. The water use figures obtained are comparable with water use figures from literatures and specifications of the respective products. Table 1 shows average water use for facilities using rainwater based on twelve months data. Since there was no treatment of the rainwater collected, therefore it is strictly used for toilet flushing, general washing and washing clothes. Table 1: Rainwater Use for various facilities Item Average daily use (litres) Average Monthly use (litres) % Washing clothes Toilet Flushing (3 W.Cs) General Cleaning (including car and motorcycle washing) TOTAL

4 Monthly Rainwater use: 13,650 liters Monthly water use (from public water supply): 27,000 liters Total Monthly Household Water Use: 40,650 liters From the above, household use for non-potable purposes using rainwater constitutes 34% of the total monthly household water use. A simulation model was developed and used to check on the reliability of the rainwater harvesting system based on the 5 m 3 and 3.3 m 3 rainwater and potable water storage tanks respectively and water demand of 455 litres/day. The start-up screen of the simulation model is shown in Figure 3. The model was run using daily rainfall data from Department of Irrigation and Drainage (DID) Ampang, Malaysia for the years 1983 to Selected rainfall characteristics at DID Ampang are tabulated below: 1. The average annual rainfall 2,542 mm 2. The highest daily rainfall 166 mm 3. The longest period without rain 29 days 4. Average period without rain 15 days Using the simulation model, the reliability of the system was found to be 65.5% and 61.4% for storages of 5 m 3 (HDPE tank) and 3.3 m 3 (brick tank) respectively and water use of 455 litres/day. Increasing the roof top catchment to 100 m 2 (utilizing the roof top for the back portion of the house at 40m 2 ) would increase the reliability to 81.5% (HDPE tank) and 75.3% (brick tank) respectively. Figure 4 shows the plot for Reliability (%) of the system for 60 m 2 and 100 m 2 Roof Catchment Areas versus various Storage Tank sizes. 4.0 ECONOMIC ASPECTS 4.1 System Cost a) The cost of the HDPE rainwater system is given below (system costs include supply and installation and vary depending on the type of materials used): Unit Amount (RM) Gutter (upvc) Conveyance System Plumbing works Water tank (top) 1 No Water tank (ground) 2500 liters capacity 2 Nos 1, Water pump (electrical) TOTAL RM 2,700.00

5 b) The system cost for the rainwater cum detention storage system (brick tank) is given below: Unit Amount (RM) Gutter (upvc) Conveyance System Plumbing works Water tank (top) 1 No Brick tank (ground) 5000 liters capacity 1 No 2, Water pump (electrical) TOTAL RM 4, Maintenance of the system Maintenance included cleaning of the rainwater collection system and chemicals to prevent mosquito breeding in the storage tank. 4.3 Unit Cost of Rainwater Unit Cost of rainwater was determined as follows:- a) HDPE tanks C - Initial Capital Cost (in Malaysian Ringgit, RM) N - Expected system life (in years) C = RM 2,700 N = 20 yrs C/N = RM Operating Cost (annual) = RM Total Annual Cost = RM Yield = 109 m 3 Unit Cost of Rainwater = Total Annual Cost/yield = RM 1.72/m 3 b) Rainwater cum detention storage tank (Brick tank) C = Initial Capital Cost (in Malaysian Ringgit, RM) N = Expected system life (in years) C = RM 4,300.00

6 N = 20 yrs C/N = RM Operating Cost (annual) = RM Total Annual Cost = RM Yield = 102 m 3 Unit Cost of Rainwater = Total Annual Cost/yield = RM 2.63/ m 3 The Water Supply Department charges piped water for domestic households at the rate of RM 1.70 for water consumption of up to 35 m 3 per household per month. It can be seen that the unit cost of rainwater at RM 1.72/m 3 (using HDPE tanks without detention storage) is comparable with the piped water cost of RM 1.70/m 3. However for the rainwater cum detention storage system the unit cost of the rainwater at RM 2.63/m 3 is much higher than the piped water. As practiced in Japan and elsewhere, the Government may need to provide subsidies to encourage the public to install rainwater cum detention storage systems. 5.0 WATER QUALITY ASPECTS Samples of the quality of rainwater collected in the storage tanks are analysed and compared with World Health Organisation (WHO) Drinking Water Quality Guidelines and Interim National River Water Quality Standards for Malaysia (CLASS 2B) as shown in Table 2. The results show that the ph which ranges from 6.26 to 6.62 (HDPE tanks) and (for brick tank) is reasonable. The hardness at between 8.6 to 32.6 (HDPE tanks) is low. The manganese (HDPE tanks) and iron contents (HDPE and brick tanks) are low as well. Toxic metals such as cadmium at less than mg/l (HDPE tanks) is below the WHO Guideline. However, lead at < 0.05 mg/l (HDPE tanks) is above the WHO Guideline. The E. Coli count at 50 counts per 100 ml (HDPE tanks) and at up to 4.48 MPN (brick tank) shows contamination from some animals/humans.

7 Table 2: Rainwater Quality in Storage Tank Interim National Parameters Units Storage tank (HDPE Tank) Storage tank (Brick Tank) WHO Drinking Water Guidelines River Water Quality Standards for Malaysia(CL ASS 2B) ph Sulphate mg/l Chloride mg/l < Silica as SiO 2 mg/l Iron mg/l Manganese mg/l Hardness as CaCO 3 mg/l Turbidity NTU Bicarbonate mg/l Nitrate as N mg/l Cadmium mg/l < < Lead mg/l < 0.05 < 0.01 Total Dissolved Solids mg/l Dissolved Oxygen mg/l Ammonia as N mg/l Total Alkalinity as CaCO 3 Coliform Count mg/l 4 18 cfu/100 ml E. Coli Count cfu/100 ml <1 27 (MPN) 0 50 < (MPN)

8 The rainwater collected proved to be of very good quality. It can therefore be used for washing clothes, car washing, plant watering, and general cleaning around the house. With low bacterial contamination the rainwater can even be used for bathing. 6.0 EFFECT OF RAINWATER CUM DETENTION STORAGE SYSTEM IN PEAK RUNOFF REDUCTION 6.1 Land use The catchment of the housing area is 7.6 ha in a predominantly residential area. The area consists primarily of double storey linked houses, shop houses, a mosque, a children s playground, a kindergarten, roads and parks/lawns. The breakdown of different land use and the area it occupies is listed in Table 3. Table 3: Breakdown of Land use in the Catchment Land Use No of units Area (m 2 ) (%) Double Storey House , Double Storey Shop 10 1, House Park/Lawn 1 16, Mosque 1 1, Play Ground Kindergarten 1 1, Roads 23, Total 76, Topography Topography in the catchment area is relatively flat. The topography ranges from 67.8 m above mean sea level (MSL) at the upstream area and 58.8m MSL at the outlet. Ground level and invert level in the drainage system are measured at site. Drain invert level shows that certain section of the drainage system is affected by accumulation of sediment. Invert level at the outlet is 57.8 m. 6.3 Drainage System The drainage system in this area is typically traditional where runoff is being disposed of as soon as possible. Runoff from the roof flows straight to the receiving drain through gutters and perimeter drains. Runoff from the roofs and roadsides combined in the road side drains and later on flow to the main drain at the outlet. Layout of the drainage

9 system, flow directions and catchment outlet is shown in Figure 5. Drains in the study area are made of concrete with concrete cover on top of it. 6.4 Brick Storage Tank The brick storage tank has a total storage of 5.0 m 3. To reduce post development peak runoff to predevelopment level (return period of 2 years), detention storage needs to be provided. In this connection, the DID Urban Stormwater Management Manual (2000) is referred to for determination of Permissible Site Discharge (PSD) and Site Storage Requirement (SSR). The SSR works out to be 1.7 m 3 (allocated for detention storage) and 3.3 m 3 is reserved for household rainwater reuse. The brick storage tank has two outlets for the purpose of storm runoff detention control. The primary outlet is through a 50mm PVC pipe with a control valve. However, the secondary outlet is a 75mm PVC pipe without any control valve. The primary outlet is located slightly above the rainwater reuse storage level whereas the secondary outlet is located 45 cm above the rainwater reuse storage level. 6.5 Simulation of the storm runoff using the Stormwater Management Model (XP-SWMM) The XP-SWMM model is used to compare the impact of detention storage provided in controlling roof runoff from the housing area. Two different scenarios were modeled to study the extent of storm runoff reduction when detention storage is provided at each house. In the First scenario, it is assumed that all the houses within the study area are equipped with the current design of the rainwater cum detention storage system. In the Second scenario, it is assumed that none of the houses in the area is installed with detention storage. The comparison is made between outflow at the outlet before installation and after installation of rainwater cum detention storage system. In this study, only runoff and hydraulic layers are used to model the surface runoff and perform hydraulic routing. A design storm having a 10 year return period (T) and 30 minute duration (D) was used to simulate the flow hydrograph at the outlet of the catchment. Two different inflow hydrographs to the drainage system were considered. The inflow hydrographs considered are the roof runoff that has to flow through detention storage and roof runoff that flows straight into the drainage system. In the case of with detention storage, the

10 reservoir routing was performed earlier and the outflow from the detention storage serves as an inflow to the drainage system. The number of houses assumed to be installed with this rainwater cum detention storage system is 242 houses with an estimated roof area of 14,520m 2 (19% of the catchment area). In the case of without detention storage, it is assumed that the generated roof runoff hydrograph flows directly to the drainage system. The inflow hydrograph to the drainage system with and without detention storage at the individual house level is shown in Table 4. Table 4: Inflow Hydrograph (from Rainwater Tank) to Drainage System at the individual house level (for Design Storm of T= 10 yr and D= 30 min) Time (min) Without Detention Storage (liter/s) With Detention Storage (liter/s) The result of the simulation shows that the peak outflow hydrograph at the outlet with detention storage is 2,562 litres/second, while without detention storage; the peak outflow is 2,837 litres/second (see Figures 6a & 6b). The peak outflow difference is 275 litres/second or about 10 percent reduction of the peak flow. This 10% reduction of peak flow is quite promising considering that only 19% of the catchment is provided with detention storage facilities. Further reduction of peak runoff could be achieved by installing rainwater cum detention storage systems in the shophouses, mosque, kindergarten and parks/lawns. 7.0 CONCLUSION The study shows that the good rainwater quality makes it suitable for a variety of nonpotable uses. The main concern in urban areas is the ph of the rainwater. A low (ph<6)

11 might make the rain water less suitable for certain delicate cleaning activities, such as car washing, where the low ph may result in corrosion of paintwork or soft materials. However, after removal of the rainfall first flush, the ph which ranges from 6.26 to 6.62 (HDPE tanks) and (for brick tank) is comparable with the WHO Guideline for piped water and is therefore suitable for any cleaning purposes. In this study the rainwater systems could meet up to 34% of the domestic non-potable household water requirements at 65.5% reliability (for storage of 5000 litres) and 61.4% reliability (for a storage of 3300 litres) respectively. The unit cost of rainwater (with detention storage) at RM 2.63/m 3 is 1.5 times more costly compared with the piped water cost at RM 1.70/m 3. The peak storm runoff reduction (when rainwater cum detention storage systems are installed at all the houses) at the catchment outlet at 10% is small and could be reduced further. The economic benefits in terms of reducing the costs of urban flood mitigation works and downstream damage reduction needs to be further investigated. Installing rainwater cum detention storage systems for other buildings/ facilities in the catchment such as at the shophouses, mosque, kindergarten and park could further reduce the peak storm runoff. Furthermore, the rainwater cum detention storage systems for the park could be used for plant watering, firefighting and emergency use for the community during a prolonged drought. 8.0 REFERENCES Adhityan Appan, Economic and Water Quality Aspects of Rainwater Catchment Systems, Proc of the Symposium on Efficient Water Use in Urban Areas, Kyoto, 8-10 June. Ahmad Jamalluddin Shaaban et al., Alternative Water Supply Options: Rainwater Harvesting, a paper presented in a Workshop on Sustainable Management of Water Resources, Shah Alam, Malaysia, 20 July. Ahmad Jamalluddin Shaaban, Zakaria Harun and Jabir Kardi, Detention Cum Rainwater Harvesting Storage System for Office Building at DID Ampang, a paper

12 presented at a Seminar on Integrated Urban Drainage Improvements for the Cities of Melaka and Sg Petani, Melaka, 5-6 June. Department of Irrigation and Drainage Malaysia, Urban Stormwater Management Manual for Malaysia. Ministry of Housing and Local Government Malaysia, Rainwater Guidelines for Installing a Rainwater Collection and Utilization System.

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