Investigation of Water Quality and Quantity of Five Rainwater Tanks in Western Sydney Australia

The use of rainwaters tank is promoted in the state of New South Wales in Australia through the BASIX initiative, which requires that all new developments be fitted with rainwater tanks. The impact of rainwater tanks are not generally considered in the design of stormwater quantity control systems; however, some studies have indicated that rainwater tanks of appropriate sizes can offer notable levels of onsite detention on top of the reduction in mains water demand. This paper describes preliminary results from a yearlong study which was undertaken to assess the overall water quantity and quality of five rainwater tanks in the Western Sydney region in New South Wales, Australia. Two rainwater tanks were continuously monitored for a full year and three other tanks were monitored on a weekly basis. Throughout the year, water quality and quantity data were collected, which were then analysed to obtain an insight into the functioning of the rainwater tanks in the study region. The results and observations indicate that `ownership' of the rainwater tank can directly influence the water use and therefore the mains water demand. It has also been found that the larger the rainwater tank, the greater the available storage within the tank prior to a rainfall event, provided the tank water is utilised sufficiently before the onset of the rainfall event. This preliminary investigation will be followed by full scale water quantity and quality modeling to determine the onsite detention and retention levels provided by the rainwater tanks and their possible impacts on urban stormwater design.