How supply system design can reduce the energy footprint of rainwater supply in urban areas in Australia

In Australia rainwater tanks are used in cities to reduce demand of mains water and increase the resilience of cities to drought. Rainwater is collected in a tank and supplied to a dwelling through a small pump. Typically the energy footprint for rainwater supply (in kWh/kL) is higher than for centralised water supply, but it can also vary markedly from dwelling to dwelling (0.4–11 kWh/kL). This study aimed to understand how the design of the rainwater supply system from the collection tank to the household can reduce the energy consumption of pumping. We examined the operation of a range of system components for rainwater supply, such as pumps, switches and pressure vessels, in a controlled residential environment (a model house) to understand their impact on the energy required for rainwater supply in urban dwellings. Results show that urban rainwater applications have flow and volume requirements which cause pumps to operate at high energy for rainwater delivery. Matching pump sizes to end use requirements and adoption of ancillary devices (pressure vessels and header tanks) have the potential to lower the energy footprint for rainwater supply. However, the energy savings can be constrained by dwelling characteristics, appliances and system design.