ECONOMIC, WATER QUANTITY AND QUALITY RESULTS FROM A HOUSE WITH A RAINWATER TANK IN THE INNER CITY Peter J. Coombes 1 , George Kuczera 2 and Jetse D. Kalma 3 1 PhD student, University of Newcastle, Callaghan, NSW, Australia 2 Associate Professor, University of Newcastle, Callaghan, NSW, Australia 3 Professor, University of Newcastle, Callaghan, NSW, Australia Abstract A dual water supply system (rainwater and mains water) has been installed at an old house in Maryville a inner city suburb of Newcastle in New South Wales, Australia. A design was developed for the installation of a rainwater tank to supply rainwater for toilet, hot water and outdoor uses. The rainwater supply is supplemented with mains water via a trickle top up system when water levels are low in the tank. An air gap is used for backflow prevention in accordance with Australian standards. The design, construction and performance of the dual water supply system at the Maryville house are examined in this paper. Monitoring of water quality from the rainwater tank and from an instantaneous hot water service at the Maryville house has revealed that the rainwater was acceptable for hot water, toilet and outdoor uses. Rainwater used in the hot water service was compliant with Australian drinking water standards. The cost of rainwater has been found to be $0.3 per kL which is less than the price of mains water in the Lower Hunter region and the commonly assumed cost of $1 to $14 per kL. Key Words: rainwater tank, dual water supply, bacteria, chemicals, costs Introduction An old house in Maryville, an inner city suburb of Newcastle in New South Wales, Australia was fitted with an above ground 9,060 Litre Aquaplate rainwater tank (area is 3.754 m 2 and height is 2.415 m) to supply hot water, toilet and outdoor uses. The house is adjacent to Newcastle’s heavy industrial area and the Industrial Highway and is situated on level ground consisting of silty-sand soil. It has a rusty galvanised iron roof with an area of 135 m 2 and the allotment area is 245 m 2 . An instantaneous gas hot water service set at 55°C is used to deliver hot water to the household that consists of an average of three people. During the working week two university students and their guests occupy the house. On weekends the house usually has four occupants (the parents of the students stay at the house on weekends). A monitoring program was established to observe water quality in the rainwater tank and at the household taps, and water use. This paper discusses the design, approval process, performance and costs of the dual water supply system. Water quantity and quality results from the monitoring program are also presented. Design of the Dual Water Supply System The dual water supply system and the locations of monitoring devices at the Maryville house are shown in Figure 1. In the design rainfall from a portion of the roof with an area of 115 m 2 is directed to the rainwater tank and supplied via a small pump directly to the hot water service and the toilet cistern. To eliminate the possibility of cross connection between the rainwater and mains water supplies the rainwater supply has been directly connected to the hot water service and the toilet cistern. Rainwater for outdoor uses is drawn directly from the rainwater tank and from mains water supply. Mains water is supplied to the remainder of the house and is used to top up the rainwater tank when water levels are low (Figure 1). The configuration of the rainwater tank in the dual water supply system is shown in Figure 2. When tank water levels are low, such as during hot, dry periods, the tank is topped up with mains water via a trickle system. The trickle top up system is expected to reduce the daily peak demand on the mains water distribution network. In the event of pump or power failure the rainwater tank can be bypassed. Design of the rainwater reuse scheme (Figures 1 and 2) makes provision for: • a minimum storage volume (to ensure that water supply is always available) • a rainwater storage volume and • an air space for additional stormwater management.