A preliminary study on the utilization of rainwater harvesting system for non-potable usage

Water scarcity is one of the major environmental issues faced by both developed and developing countries worldwide including Malaysia. Water shortage issues generally occurs due to increasing of water demand in line with the population growth, inadequate water supply, high domestic water consumption and others. Water conservation using rainwater harvesting system (RWHS) is a key strategy to overcome the consequences of water shortage and minimize the dependency on main water supply. Several commercial and residential buildings in Malaysia have employed the RHWS as alternative to the main water supply but the implementation is not widely made. This study is focusing on the utilization of collected rainwater using RWHS in local mosque for non-potable usage including toilet flushing and garden watering. Rainwater was collected for three rainfall events and was tested for six (6) water quality parameters namely pH, turbidity, total dissolved solids (TDS), total suspended solids (TSS), E. coli and total coliform. The water quality analysis showed that the values of the pH, turbidity, TDS, TSS, E. coli and total coliform were in the range of 6.9 - 8.2, 2.67 - 8.41 NTU, 6.7 - 24.1 mg/l, 4.0 – 39 mg/l, > 2419.6 and > 2419.6 respectively. Based on the recommended raw water quality criteria, all parameters are within the safe limit for non-potable usage. However, treatment is required if the collected rainwater will be used for potable usage in future. In the other hand, the optimum size of RWHS tank is determined based on the estimated water demand using the MSMA 2nd Edition and the efficiency was assessed using the Tangki NAHRIM 2.0 simulation model. Data analysis from Tangki NAHRIM 2.0 showed the water saving efficiency, storage efficiency, average annual volume of spillage and yield and percentage time tank was filled with varying percentage of rainwater. At the optimum RWHS tank size of 6 m3, the water-saving efficiency and storage efficiency are 56.9% and 35.5% respectively.Consequently, utilization of rainwater harvesting methods for domestic, landscaping and agricultural activities will help to minimize the demand for treated water supplies.