Reliability analysis for rainwater harvesting system in peri-urban regions of Greater Sydney, Australia

Rainwater harvesting has become quite popular in Australia in recent years. In metropolitan areas, rainwater tanks are used to save mains water, but in peri-urban and rural areas, rainwater tanks are used as the principal water source to many households. In this case, the reliability of rainwater tank to meet given water demand is important. This study presents development of a rainwater tank model that can determine the tank size which can meet the most of the water demand in peri-urban areas. The model is a continuous simulation type, with daily time step. The model is applied to 10 different locations in Greater Sydney and assesses the feasibility of 8 different rainwater tank sizes, 1 kL to 20 kL. Nine of these ten locations are situated in the peri-urban areas of Greater Sydney, which are Campbelltown, Hornsby, Penrith, Richmond, Castlereagh, Wallacia, West Pennant Hills, Moss Vale, and Cataract Dam. The other location (Parramatta) is situated in the approximate centre of the Greater Sydney, which is used for bench marking the water use in peri-urban and metropolitan Sydney regions. The daily rainfall data at each of the ten selected locations was obtained from the Australian Bureau of Metrology. The rainfall data lengths were in the range of 31 to 150 years, with an average of 73 years. It has been found that for toilet and laundry use, a 7.5 kL tank can meet almost 100% of the demand, but to meet the irrigation demand, a much larger tank is needed. It has been shown that irrigation demand cannot be met 100% even with a tank size of 20 kL. The method presented in this paper can also be applied to other Australian states and countries to estimate water savings and reliabilities of rainwater harvesting system using daily rainfall data