Do Rainwater Tanks Punch above Their Weight?: The Use of a Probabilistic Distributed Demand Model to Estimate the Contribution of Decentralised Water Sources to Supply Security

There has been significant debate recently about the contribution of rainwater tanks to water supply security. Traditional thinking was that in the middle of a drought when the water was needed, the tanks were all empty. In the rawest form of economic analysis, the total cost of storage in dams and tanks is directly compared with tanks understandably coming off second best. In recent years, work has shown that rainwater tanks can make a contribution to supply security because of their remoteness from surface water supply catchments and the responsiveness of their roof catchments. In this paper, the contribution made by rainwater tanks to supply security is examined from a total system perspective using a probabilistic distributed demand model. The total cost of providing water supply is compared for a hypothetical city with and without rainwater tanks. The cost-effectiveness of rainwater tanks is estimated by comparing with and without cases.