Cost-Benefit Analysis for Rainwater Tanks in the Sunshine Coast Planning Scheme
Natural Capital and Climate (NCC) prepared a cost-benefit analysis for Sunshine Coast Council to assess the community-wide impacts of requiring rainwater tanks in new class 1 dwellings under the proposed planning scheme. The analysis examined water supply, stormwater management and broader environmental outcomes, demonstrating a positive net benefit to the Sunshine Coast community.
Assessing the value of rainwater tanks for future water security
Population growth and climate change are placing increasing pressure on water supply infrastructure across the Sunshine Coast. Most residential dwellings in the region are connected to the South East Queensland water grid, which faces growing demand and potential long-term reductions in climate-dependent water yields. In response, Sunshine Coast Council considered requiring rainwater tanks in new class 1 dwellings as part of its proposed planning scheme and required a cost-benefit analysis to support the policy proposal.
Natural Capital and Climate was engaged to undertake a robust cost-benefit analysis to determine whether a rainwater tank mandate would deliver net benefits to the Sunshine Coast community. The assessment applied a triple bottom line framework and examined potable water substitution, reduced requirements for alternative stormwater treatment infrastructure, and, where possible, broader environmental and community outcomes associated with reduced stormwater runoff. These included potential improvements to waterway stability, nuisance flooding, drainage issues and urban cooling.
The analysis found that implementing rainwater tanks as a requirement for new class 1 dwellings would generate positive net benefits for the community, with an estimated net benefit of $1.4 million and a benefit-cost ratio of 1.02. Benefits were found to accrue primarily to households through reduced water bills and the non-market value of avoiding restrictions on outdoor water use. Additional benefits were identified through lower stormwater management costs, which ultimately benefit residents.
The study also found that climate change is expected to have a negligible impact on rainwater tank yields, making them a relatively resilient supplementary water source. While rainwater tanks are not expected to replace major supply infrastructure, they can make an important contribution to local water security, particularly by supporting non-potable water use during periods of water restrictions. The analysis noted that several benefits could not be quantified, including some flooding and urban amenity outcomes, suggesting the total community value may be greater than the quantified results indicate.
