Project Date: 31 December 2014
Project Status: Complete
Research Organisation: CSIRO
Project Number: 10TR4 - 001
Rainwater tanks are private assets that provide public benefits. However, poorly maintained rainwater tanks may have very little benefits and may even increase health risks. Unfortunately not enough information is available on the condition of these private assets; and further information is needed to estimate water savings and stormwater related benefits. This project addresses these knowledge gaps.
The project included two key activities: 1) a survey of conditions of rainwater tanks; 2) a metering study of 21 rainwater tank systems. The study was required to comply with the NHMRC National Statement on Ethical Conduct in Human Research.
The survey of 417 household rainwater tank systems includes tank condition inspections and questionnaires and was undertaken across the Metropolitan area as defined by the operational areas of the three major Melbourne water retailers. The majority of the tanks (62 per cent) were installed between 2007-2010 during the peak of the drought and the severe water restrictions levels. Some important results are that many automatic mains switches are not working. Nine per cent of all sites had faulty electronic diverters. 5 per cent of all sites had pumps that were not working. 39 per cent of sites had lead flashing on the roof. 19 per cent of water samples had an odour, and 57 per cent of water samples had some level of discoloration. 12 per cent of sites had mosquito larvae present in water or mosquitoes present in tank. Only about half of all sites had foundations that were level, and six per cent of sites had foundations which were deemed to be hazardous. 13 per cent of tanks were leaning against objects. However, most participants (96 per cent) see benefits with their tanks; of which the most prominent reported benefits were to allow watering during restrictions (88 per cent), to reduce water consumption/bills (82 per cent) and provide benefits for the environment (71 per cent).
The metering of rainwater use occurred in 21 sites across Melbourne. The study was undertaken was similar to that of a previous study in South East Queensland as part of the Urban Water Security Research Alliance. The participants in the metering study were primarily staff members at the Melbourne water companies. The rainwater use in the different sites varied considerably depending on the setup. External only sites (6 sites) had an average rainwater use of 11 kL per annum. The 4 indoor only sites had an average rainwater use of 31 kL. The sites where rainwater was used both for indoor and outdoor purposes had an average rainwater use of 42 kL after compensating for automatic switch malfunctions. It is also noted that in four of the metered sites (19 per cent of sites), automatic switches were either broken or turned off; and this significantly impacted on the results. The average specific energy for the pump was 1.7kWh/kL.
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