Energy and economic impacts of rainwater tanks on the operation of regional water systems

This study has analysed the reductions in operational costs (pumping, water treatment and maintenance) and greenhouse gas emissions from regional water supplies that include installation of rainwater tanks used to supply domestic laundry, toilet and outdoor water uses across New South Wales. The household cost of rainwater supply ranged from $7.95/kL at Broken Hill to $0.88/kL in the Central Coast region. However, installation of rainwater tanks produced considerable reductions in operating costs of a city’s water system ranging from $57 to $6371 per household installing a rainwater tank. Significant reductions in greenhouse gas emissions of up to 75% from including rainwater tanks in regional water systems were also observed. In addition, significant improvement in the security of regional water supplies with subsequent deferral of the requirement for augmentation of supply (new dams or desalination plants) was observed for coastal cities. These benefits were seen to be dependent on the average annual rainfall depth, distance from the coast, and availability of reliable operational and augmentation data of a regional water system. This study reveals the importance of including rainwater tanks or, indeed, any other decentralised water management option in analysis of the operation of regional water systems to provide a realistic understanding of combinations of centralised and decentralised water management strategies.