Energy intensity of residential rainwater tank systems: exploring the economic and environmental impacts

This paper investigates the energy intensity of residential rainwater tanks and attempts to assess the implications of this energy consumption on the merits of these systems as a whole. The use of decentralised water supply systems has been encouraged in urban areas through legislation and state based incentives in many parts of the world. However, there has been a lack of empirical field research detailing the end-use energy consumption of these systems, and consequently a lack of understanding surrounding the impact their energy consumption has on their overall viability as a water supply source. This research examines high resolution, end-use level water and energy data from an internally plumbed rain water tank system (IPRWTS) monitoring study recently concluded in South-East Queensland, Australia. This data is then used to inform life cycle simulation and analyses. The findings indicate that the IPRWTS configurations in the case-study location have marginal cost-benefit and that significant cost differences arise in identical systems, due to pump performance factors. An unexpected finding was that in nearly half of the monitored homes, pumps were consuming large amounts of energy in frequent re-pressurisation of pipe systems, leading to increased electricity costs for householders. Analysis demonstrates that pump selection and the end-uses plumbed into the IPRWTS are important considerations in order to optimise cost-benefit. Quantification of these relationships gives homeowners, builders and policymakers the opportunity to improve decision making when implementing IPRWTS in residential homes.