Rainwater - A Feasible and Economic Solution to the Acute Drinking Water Shortage of the Slam Dwellers of Dhaka City

Transcription

1 Rainwater - A Feasible and Economic Solution to the Acute Drinking Water Shortage of the Slam Dwellers of Dhaka City Islam, M. M. 1, Kabir, M. R. 2 and Chou, F. N.-F. 1 1 Dept. of Hydraulic and Ocean Engineering, National Cheng Kung University, Tainan, Taiwan ( manzurul73@gmail.com; hyd4691@mail.ncku.edu.tw) 2 Dept. of Civil Engineering, The University of Asia Pacific, Dhaka, Bangladesh ( mkabir_uap@hotmail.com) ABSTRACT The shortage of safe drinking water sources is increasing whole over the world. A good many prominent people have recently forecasted that wars of the 21 st century will be fought over water not on oil. Thus, water as a safe drinking water as well as some other important uses like cooking, dishwashing etc. is a very important component for daily life. But the safe water for the above mentioned uses is not always available due to shortages of surface water, groundwater contamination (arsenic, manganese and uranium contamination), groundwater depletion and so on. A research work had conducted to collect and store the rainwater for medium term in a ferrocement storage tank. To examine the quality of the stored rainwater, some physical, chemical and bacteriological parameters were tested once in every 15 day throughout the storage period. The quality of stored rainwater was within the acceptable range for drinking purposes up to three months. After that period a few numbers of total coliform was detected. A cost-benefit analysis was performed to compare the installation and maintenance cost of the rainwater harvesting system with the existing water supply system and found that the rainwater system was more economic. From the quality and the economic point of view, a questionnaire survey study was conducted on four slam areas of Dhaka City to get the dwellers opinion on rainwater system. The study revealed that the rainwater was acceptable to the slam dwellers not only economic point of view but also quality point of view. Keywords Cost-benefit analysis; feasible; ferro-cement; rainwater; storage tank. INTRODUCTION The pressure on water resources is increasing as the economic condition and the consumption per capita increases, populations grow through world-wide and its impact is not very satisfactory. To meet the water shortage, different types of water usage like drinking, cooking, dishwashing etc. which are significant components of domestic water demand, could be fulfilled using rainwater. The countries where the rainwater is ample, it can be satisfied in partly or in fully if it is collected properly. Dhaka City is one of many mega cities (i.e., cities with population exceeding 1 million; Karn and Harada 21) is facing a severe shortage of safe drinking water. Only 75% of its total demand can be met through the centralized piped system, out of which 83% of that water is supplying from ground water which is not pleasing at the moment. The groundwater table of Dhaka City is depleting on an average 1-3 meters/year. Remaining 17% is providing from surface water bodies comprising the peripheral rivers around the Dhaka City treated by water treatment plants before entering the distribution system (Rahman and Hossain, 28). In the next 2 years, Dhaka City is projected to have a population of about 2 million (BBS, 1998). This population growth would

2 create an extra water supply demand of 42% which has to be met either from the surface water sources or by sinking additional deep tubewells (DTWs) or using alternative potential source. The Dhaka Water Supply and Sewerage Authority (DWASA) is entrusted with supply of piped water in the Dhaka Metropolitan and its peripheral area. This groundwater source which is a major part to supply the Dhaka City s demand is limited. In most parts of the City, the groundwater abstraction exceeds the recharge rate, causing the groundwater to be mined systematically and be depleted of its reserve. The present rate of depletion is alarming because it can potentially cause environmental hazards such as land subsidence, prolonged water logging, alteration in vegetation etc. (Kabbour and Zouhri 25; Karami and Hayati 25). The everyday electricity demand shortage in Dhaka City is around 5 MW which is hindering to pump underground water. On the other hand, the water supply line of Dhaka City is old as well and in some places the water supply line and sewerage line connected together and the supply water reached beyond the usable condition. It affecting the dwellers to get water borne diseases and also getting unexpected bad smell which is not acceptable. Dhaka City is surrounded by Turag River, Tangi Canal, Balu River, Shitalakhya River, Dhaleshwari River and Buriganga River. However, the surface water of these peripheral rivers is known to be highly polluted due to municipal and industrial untreated wastewaters including heavy metals that are discharged. Sometime especially during dry season, the pollution level of these water bodies is going beyond the treatment level and the treatment cost is increasing day by day. There are four surface water treatment plants exist in the Dhaka Metropolitan area. Among them, three located in the Dhaka City Corporation (DCC) area, while one is located in the Narayangonj Municipality. The volume of water treated by these plants is small compared to total demand of water supply. On the other hand, water quality of the Buriganga and Sitalakhya is deteriorating fast which will not be suitable for treatment for potable water supply in the near future. So, DWASA is considering Meghna and Padma Rivers will be the potential sources of water source for the water treatment plants to supply water for the Dhaka City. Getting surface water from those rivers would be very expensive and time consuming. Thus, there is an urgent need to mitigate the present demand using different water bodies and explore more sustainable sources to augment the present and future water supply. One potential solution is the use of rainwater to reduce the shortage of safe drinking, cooking and dishwashing purposes (Islam, 21). Many agencies, including the DWASA are studying the feasibility of rainwater harvesting as alternative source of water and a way to recharge the depleted groundwater table. Institute of Water Modeling (IWM) had conducted a study on the possibility of rainwater harvesting in Dhaka City and it was revealed that Dhaka city is situated on around 37 sq km of land with a roof area of 75 sq km as there are around 675, concrete houses in the city. With the current amount of rainfall, IWM estimated that around 149,16 million liters of water could be harvested during the monsoon. From the literature it was found that the everyday demand for the City is around 2,1 million liters per day (mld) of which around 1,5 mld is supplied by DWAWA and 31 mld is supplied by the surface water (Asia Water Wire, 25). The estimated rainwater can supplement to the existing supply system as a potential alternative water source to reduce the acute water shortage. NGO Forum, BRAC, Plan Bangladesh and a lot of NGOs are working to implement the rainwater harvesting system as alternative source and their progress is not satisfactory considering to the fulfillment of the demand. World Bank, Asian Development Bank and some other development partners are providing fund through Bangladesh Government and some NGOs as well to make the system effective. METHODOLOGY

3 Description of the Study Area A research work had conducted at the campus of Bangladesh University of Engineering and Technology (BUET), Dhaka, Bangladesh (23 42'"N 9 22'3"E) to store rainwater for duration of four months. To provide stored rainwater of a family consisting five members during dry season, a ferro-cement storage tank having the capacity of 3.2 m 3 was constructed at the study area. During the rainy season the users of the tank would use rainwater directly and for the dry period, the rainwater would be stored to the tank for a medium term (4 months) period to satisfy the demands of only drinking, cooking and dishwashing. The tank was constructed at BUET campus for better monitoring and maintenance purposes and its proximity to the testing laboratory of Department of Environmental Engineering, BUET, Dhaka, Bangladesh. Four slam areas of Dhaka City were selected to conduct a survey to get the dwellers willingness towards the rainwater harvesting system (RWHS). Questionnaire Survey For the present study, four slams of Dhaka City such as Kathal Bagan and Nakhalpara were from new Dhaka City (ward nos. 8 and 48); Rahmatgangj and Namapara were from old part of Dhaka City (ward nos. 16 and 3) were selected. Before launching the field survey, a preliminary reconnaissance survey of the study area had conducted whether there is any existing supply system provided by either DWASA or other organizations. After selecting the survey areas, a household survey was conducted as the sample study. Approximately 4% of the households from the survey areas were selected for field survey. All together 2 households were taken for questionnaire survey. To fulfill the objectives of the study, a questionnaire was formulated. The questionnaire was divided into two major parts; The first part was designed to identify the household information, housing, sanitation, health facilities, ownership of slams etc. and the second part was to identify the existing water supply, bottleneck of the existing system, water demand, present water use rate, knowledge on rainwater harvesting system and acceptability of rainwater harvesting technique etc. The questionnaire was structured and pre-coded with multiple choice type of answer. Rainfall Analysis The climate of Bangladesh is characterized by high temperatures, heavy rainfall, often excessive humidity and fairly marked seasonal variation. Rainfall occurs in Bangladesh due to north-easterly winds during the rainy season, and annual rainfall varies from 125 cm to 35 cm. Rainfall data from 1957 to 1996 were analyzed, and the 7-day and 1-day minimum dependable (9%) rainfall of Dhaka City were considered. A mass curve analysis was performed to know the availability of the rainwater to support drinking, cooking and dishwashing purposes. From the questionnaire survey, the actual water demands for different components like drinking, cooking and dishwashing were determined. The mass curve analysis had performed using those actual demands. Determination of the Storage Tank Volume and its Construction The volume of the storage tank was determined using the Area consumed (A c ) - Volume consumed (V c ) relation method. Required volume was calculated using such water use variables as drinking, cooking and dish washing. In this method, a relationship between critical catchment area per person (m 2 per capita) and minimum storage volume provided per person served (m 3 per capita) was determined based on a series of N year actual monthly rainfall data and a selected frequency of periods with limited supply. This method requires a series of calculations which is explained by IWACO BV, (1981). A ferro-cement tank was constructed according to the specifications and guidelines mentioned by Islam (21). Water Collection Procedure and Sampling After completion of the tank construction, a non-toxic water-proof cloth (catchment) was set above the tank. The water-proof cloth was used as a test case because the houses roofs are mostly

4 constructed by the materials, are not suitable to collect good quality rainwater. An initial flushing device developed by Islam (21) to divert the dirty water from the first rainfall and a plastic net to remove the leaves or other matter were attached at the inlet of the storage tank. This rainwater collection procedure was initiated on September. Sampling of stored rainwater was performed eight times throughout the four-month storage period after filling the tank. Some physical, chemical and microbiological tests were conducted according to the standard methods for the examination of water and wastewater (APHA, 1998). Cost-Benefit Analysis Different materials can be used for gutters and first flush and required materials depend on the roof size. The Table 1(a) and 1(b) give the costing of gutters and first flush at previous and present market price. The bamboo made gutters and first flushes have short life span. It can work properly for one rainy season. Again, leakage is a major concern in case of bamboo and wood made gutters and first flushes. The cost of G. I. pipes is very high comparing to other materials. PVC pipes are very cheap and readily available at the rural areas of Bangladesh. The PVC pipes should be used as gutters and first flushes for rainwater harvesting system in the rural areas of Bangladesh. Table 1 (a): Costing of Gutters and Flushing device (Ferdushi, 1999). Materials Total cost, Tk. (48.5 Tk. = 1 US $) Bamboo made 22 Wood made 64 PVC pipes 74 G. I. Pipes 224 Table 1 (b): Costing of Gutters and Flushing device considering present market price Materials Total cost, Tk. (68.5 Tk. = 1 US $) Bamboo made 42 Wood made 15 PVC pipes 124 G. I. Pipes 53 Some potential materials for storage tank have been selected. These can be applied in different sizes in the rural and urban areas of Bangladesh. No fixed design or materials were selected on the basis of literature review, as these technologies require field-testing at the rural context of Bangladesh. The costing of storage tanks having different materials is given in Table 2(a) and 2(b). From the tables it was clear that the costing of the ferro-cement tanks was cheaper than the other materials like steel sheet or plastic. On the other hand the durability of the ferro-cement tank is also high compared to other materials. The construction technology is also simple and local masons can construct it easily after getting a short demonstration. So, the ferro-cement tank was selected for the study as it was cheap and the construction materials are easily available. Table 2 (a): Costing of storage tank (Ferdushi, 1999), (48.5 Tk. = 1 US $) Materials Capacity (m 3 ) Total cost (Tk.) Unit cost (Tk.) Ferrocement molded tank Ferrocement wire framed tank Ferrocement bamboo reinforced tank Cement jars Cement ring tank Brick reinforced tank

5 Table 2 (b): Costing of storage tank considering present market price (68.5 Tk. = 1 US $) Materials Capacity (m 3 ) Total cost (Tk.) Unit cost (Tk.) Ferrocement molded tank Ferrocement wire framed tank Ferrocement bamboo reinforced tank Cement jars Cement ring tank Brick reinforced tank Steel sheet tank Steel sheet tank Plastic tank Cost-benefit analysis was performed using different water demands and corresponding sizes of the storage tanks for different purposes such as (i) drinking, (ii) drinking and cooking, (iii) drinking, cooking and dishwashing. Based on the market price, the cost effectiveness of optimum size of the constructed (ferro-cement) tank was also analyzed in comparison to plastic and GI tanks. Cost effectiveness analysis on the existing water supply system (DWASA) and the rainwater harvesting system were analyzed to compare the unit production cost between the two systems. RESULTS AND DISCUSSIONS A questionnaire survey was conducted to get people s perception about the existing supply system, the rainwater harvesting system and the willingness towards the rainwater harvesting system. Only a few of them which were very important for this study, are described below step by step. From the survey report it was revealed that the water demand for the four different slam dwellers were not same but a little difference. Considering their demands and according to 4 years rainfall data the supply/demand curves and the different demand components were drawn which is shown in Figure 1. The catchment area for collecting the rainwater was used 2 sq. m for this analysis. From the figure it was confirmed that the supply water by rainfall was well enough to satisfy the water usage components for each and every slam areas which were surveyed for this study. Supply/Demand (lit) Kathalbagan S D D+C D+C+DW Supply/Demand (lit) Nakhalpara S D D+C D+C+DW Days Days Supply/Demand (lit) Rahmatganj S D D+C D+C+DW Supply/Demand (lit) Namapara S D D+C D+C+DW Days Days

6 Figure 1: Supply/Demand curve for different water use components for four survey areas A question was set to get the dwellers perception about the existing system s water use rate/price and the analyzed results are shown in Figure 2. The options for answer were very high (if the rate >.25 Tk./l), high (if the rate.15~.25 Tk./l), normal (if the rate.5~.15 Tk./l) and no response. 54% dwellers from Kathalbagan area opined the rate is normal. But the majority dwellers from other three areas opined that the rate is high. The overall result shows from the figure that 45% of the dwellers opined that the WASA water use rate was high and they were not satisfied at all on the system because of high rate. Rate of WASA's water Price/rates of WASA's water supply Very high (>.25 Tk/l) High ( Tk./l) Kathalbagan Nakhalpara Rahmatganj Namapara Total Area Normal (.5-.15Tk./l) No response Figure 2: Price/rates of WASA's water supply Table 3 describes about the amount of money, the dwellers willing to pay to use the rainwater harvesting system. It was found that the highest number i.e., 42.5% dwellers from Namapara were willing to pay BDT 3/month where as the second highest 42.14% from Kathalbagan were agreed from the same amount. From the table, it was revealed that 38.61% people were interested to pay BDT 3/month if they could get the rainwater harvesting system to use it as a safe drinking water. Table 3: Willing to pay for rainwater Taka per Study area month/family Kathalbagan Nakhalpara Rahmatganj Namapara Total % 5.9% 22.14% 12.5% 12.46% % 3.9% 24.29% 27.5% 25.67% % 3.45% 39.29% 42.5% 38.61% % 9.9% 4.29% 5% 7.45% % 3.64% 1.43% % > N/A 14.29% 2% 7.14% 7.5% 12.23% NR % 5% 1.6% Total 1% 1% 1% 1% 1% The overall acceptability of the rainwater harvesting system was reviewed to the selected slam dwellers. The survey results were analyzed and presented in Table 4. From the table, it is found that the majority dwellers from all of the slams opined about their acceptability and the range was 4 to 6 percentages. The highest 58.18% from Nakhalpara mentioned that the system is acceptable to them and the range was 4 to 6%. A total of 52.5% dwellers were interested to use the rainwater harvesting system and their acceptability range was 4% to 6%. Table 4: Overall acceptability of rainwater harvesting techniques

7 Location Percentage < No res. Total Kathalbagan 2.86% 2% 42.86% 14.29% 5.71% 14.29% 1% Nahkhalpara % 58.18% 7.27% 5.45% 3.64% 1% Rahmatganj 5.71% 15.71% 55.71% 8.57% 8.57% 5.71% 1% Namapara 7.5% 17.5% 42.5% 12.5% 1% 1% 1% Total 4% 19.5% 52.5% 1% 7.5% 7.5% 1% The cost comparison for the rainwater harvesting system and the existing water supply system is shown in Table 5. The construction cost for the rainwater harvesting system was considered BDT 1, which was found for ferro-cement tank having capacity of 3.2 m 3 for a family consisting 5 members. The economic life was considered 15 years for the ferro-cment tank and the annual repair and maintenance cost was BDT 2. The first flush and gutter system (for PVC) cost was BDT 1,24. The total cost for the system was BDT 14,4, annual payment was BDT 936 and the water cost was BDT.99/liter. The connection cost for the existing water supply system was BDT 1, and the water use rate BDT.15~.25/liter. Considering the same 15 years, the annual payment was calculated as BDT 2,9. It is revealed that the rainwater harvesting was more economic than the existing supply system. Table 5: Cost comparison between rainwater harvesting system and the existing supply system Rainwater Harvesting Technique Existing WASA water Cost: Total construction cost Tk. 1, + Tk. 1,24 for gutter and first flush. Maintenance cost Tk. 2/year (including cleaning by chlorine and repairing if any leakage detected) Economic life = 15 years Therefore, total cost = (1, + 1,24+ (2 x 14)) = Tk. 14,4 Annual payment = (14,4/15) = Tk. 936 Cost/liter = 14,4/(26 lit x 365 days x 15 years) = Tk..99/litre Cost: Connection cost = Tk. 1,/connection Water use rate = Tk..15 to Tk..25/litre. Total cost = (Tk..15 x 26 liters x 365 days x 15 years) + 1, = Tk. 31,352.5 Annual payment = (31,352.5/15) = Tk The physical and chemical tests were performed for color, total solids, total dissolved solids, lead, turbidity, hardness, acidity, ph, nitrate and fluoride. The chemical analyses were conducted according to the standard methods for the examination of water and wastewater (APHA, 1998). On the other hand, microbiological tests were performed for total coliform (TC), fecal coliform (FC), COD, and BOD. Each water sample was tested for TC and FC following procedures described elsewhere (APHA 1998). The test results were within the acceptable range except the total coliform. After three months, total coliform levels were 8, 9 and 11 per 1 ml in the 6 th, 7 th and 8 th test results respectively but these levels were low risk level designated by WHO (1993). CONCLUSIONS From this research, it was clear that for the water scarce areas, the rainwater harvesting was a very useful and acceptable as low cost technique. Also in the scarce safe drinking water areas like Dhaka, it might be very useful. The water quality was acceptable as safe drinking water in Dhaka areas up to four months and it was applicable only for this area, because the air quality of the other cities might

8 not be the same. So, the rainwater quality might differ. The cost for using rainwater was acceptable to the dwellers. To use this potential source to the dewllers, Government needs to implement some rules, make awareness about the safety of RWHS through mass media campaign. A lot of NGO s are now working throughout Bangladesh and Government should introduce a website collecting all the related updated sporadic information from different working groups and make readily available to the dwellers. A different and independent department could be setup using different ministries and divisions joint collaboration like: Economic Relations Division, Ministry of Planning, Ministry of Information, Ministry of Housing and Public Works, Rural Development and Cooperative Division, Local Government Division and Ministry of women and Children Affairs. The department would include research and innovation division to find out the proper implementation mechanism of the rainwater harvesting system. REFERENCES APHA, AWWA & WEF, (1998), Standard Methods for the Examination of Water and Wastewater, (Eaton et. al. Editors), American Public Health Association, American Water Works Association, Water Environment Federation, 2 th Edition. Asia Water Wire, Bangladesh Bureau of Statistics (1998) Pocket Handbook, published annually by the Government of Bangladesh (available online at last accessed February 2, 27). Ferdausi, S. A., (1999), "Study of Low-cost Arsenic Mitigation Technology for Application in Rural Bangladesh", M.Sc. Thesis, IHE, DELFT, The Netharlands. Islam, M. M., 21. Study on Rainwater Harvesting Techniques. M.Sc. Engineering Thesis, Department of Water Resources Engineering, Bangladesh University of Engineering and Technology, Dhaka, Bangladesh. IWACO BV (1981), "Design manual on rainwater harvesting systems", Project 545. Kabbour, B.B., and Zouhri, L., 25. Overexploitation and continuous drought effects on groundwater yield and marine intrusion: considerations arising from the modelling of Mamora coastal aquifer, Morocco. Hydrol Process 19(18): Karami, E., and Hayati, D., 25. Rural poverty and sustainability: the case of groundwater depletion in Iran. Asian J Water Environ Pollut 2(2): Karn. S.K., and Harada, H., 21. Surface water pollution in three urban territories of Nepal, India, and Bangladesh. Environ Manage 28(4): Rahman, S., and Hossain, F., 28. Spatial Assessment of Water Quality in Peripheral Rivers of Dhaka City for Optimal Relocation of Water Intake Point. Water Res Man, 22: WHO 1993, Guideline for the Drinking-water Quality, (2 nd Organization, Geneva, 188p Edition), Vol.1, World Health