Developing design curves for rainwater harvesting in Greater Sydney

![CDATA[Rainwater tanks are an important component of Water Sensitive Urban Design (WSUD) as they reduce potable water demand, remove pollutants from urban run-off, offer a greater resilience to the urban potable water supply system and have the ability to provide stormwater drainage relief. The design of an efficient and cost effective rainwater harvesting (RWH) system depends on various factors including roof catchment size, water demand, local rainfall and loss characteristics of the roof catchments such as gutter overflow and depression losses. In practice, a 3 kL tank size is commonly used in Sydney for a detached residential house, but to achieve maximum benefit from a RWH system in a given region, it is desirable to design the system based on site conditions and other relevant design parameters. This paper presents the development of simplified design curves to optimise RWH system design for the Greater Sydney region in Australia based on a daily water balance model. It uses data from 159 rain gauge locations across Greater Sydney. It has been found that there is a great variation in annual rainfall across the selected locations and that a common optimum tank size cannot be selected for Greater Sydney region. It has been shown that there is a moderate correlation between the tank reliability and mean annual rainfall. A 5 kL tank can achieve a reliability of 31 – 93 % for 4 people depending on the location in Greater Sydney, site areas and the types of water use.]]