There is a common perception that rainwater harvesting (RWH) is an environmentally sustainable water supply option. This perception is not always precise for all arrangements of the RWH system and components. Thus, all potential features of RWH need to be thoroughly studied to verify its environmental impacts. Broadly, on a household-scale RWH, there are two LCA aspects available in the literature, which can be identified as selecting tank material on the one hand and saving potable water on the other hand. Most of these studies used HDPE as tank material and its fabrication, transportation, installation, and disposal. However, the effects of yearly runoff and pollutant load reductions in net environmental impact assessments were not included in those studies. In this study, catchment-scale net environmental impacts of RWH systems made of different tank materials (e.g. HDPE, LDPE, ferrocement, and steel), components (with pump, no pump, and raised tank bases), tank and roof sizes, and varying annual rainfall patterns (e.g. dry, average and wet years) for various RWH supply reliabilities, were quantified through LCA approach. Results show that the HDPE tank has lesser impacts in most of the impact categories than other tanks. RWH systems with tank sizes of 2000 and 3000 L without pumps, and tank size of 2000 L with a pump under 150 m2 roof, are the most feasible environmental perspectives. The water-saving and pollutant load reductions cannot compensate for the pump operation's impacts, except for very few cases, like 2000 L tank during the driest rain year at lower reliabilities. A tank size larger than 2000 L would not be effective. On average, 70% of the total net life cycle impacts were developed from the operational phase of the RWH (with a pump). The pumping operation provided about 6.5 times higher CO2-eq emission than the watermain. The outlined strategy would help select tank materials, sizes, and RWH accessories based on annual rainfall and roof size available and introduce definite engineering standards, government rebates, and guidelines for RWH. This approach of quantifying the environmental impacts will explain further insights into the RWH system and its components.
