This report summarises the results of a physical on-site assessment of the household rainwater tank systems of 223 Class 1 dwelling sites with mandated rainwater tanks in four Local Government Areas (LGA) (Pine Rivers, Caboolture, Gold Coast and Redland) in South East Queensland (SEQ). In this on-site inspection, rainwater tank system installation aspects were assessed in relation to the requirements of the Queensland Development Code (QDC) Mandatory Part (MP) 4.2 – Water Savings Targets (2007) in order to determine if there are any installation factors which may impact on the usage and performance of rainwater systems in attaining the 70 kilolitres/household/year (kL/hh/yr) water savings target for Class 1 detached dwellings. The three main installation requirements of MP4.2 for achieving the water savings target relate to: rainwater tank storage capacity, roof catchment area and connection to appliances.The results of the on-site assessment revealed that:•installed rainwater tank storage capacity per site is mostly above the required 5,000L, although 16 percent of sites inspected had storage volumes of below 5,000L; •roof catchment area does not meet requirements in 40% of cases, either in terms of having 100m² or 50% of total roof area, connected to the tank; and•connection to toilets, washing machine and external tap meets requirements in most cases.In addition, the study has concluded that in estimating effective tank volume from manufacture’s claimed volumes, claimed volume should be reduced by about 10% to account for the dead volume below the outlet level and by about 20% if pump cut-off factors are also included. In the absence of claimed volumes, storage volumes can be calculated using gross physical tank dimensions, but should first be reduced by about 12% to account for volume lost due to tank shapes which generally round off edges and are not perfectly square or round.In view of the importance of connected roof area in achieving mains water savings, of greatest concern, is across the board level of non-compliance in terms of roof area catchment connected to the rainwater tank system, which can be claimed with a reasonable degree of confidence. Even relaxing the level of compliance to within a 20% variance, does not significantly improve the prognosis. Certainly, in any policy and management intervention to improve the yield from rainwater tank systems in SEQ, this aspect of increasing the area of roof catchment connected to the rainwater tank is the single most important physical installation factor to be considered. Specification of roof area to be connected rather than percentage of roof area to be connected emerges as a more easily achievable target.
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