The global freshwater crisis and its associated risks have been greatly appraised. Many of the worlds developed nations are faced with water supply and quality dilemmas, while more than one billion people in the developing world are without consistent water supply (WWAP, 2012). In Australia, the availability of freshwater is expected to decline due to climate change (CSIRO, 2011), while demand for the water is set to increase under a growing population (Pink, 2010). This supply-demand gap means that new sources of water must be identified, evaluated and developed. It must be considered that water supply systems are not only impacted by climate change, but that they also contribute to it through the consumption of energy (Flower et  al. 2007). This energy-water-climate nexus dictates that water supply systems that are selected to augment traditional reservoir-based supply must both provide water and consume energy efficiently to achieve sustainability. Internally plumbed rainwater tanks (IPRWT), supplying water to residential households, are a member of the alternative water supply source spectrum. IPRWT systems typically contain a pump to generate the necessary flow and pressure required for water end-uses in and around the home. Consequently, these pumps are responsible for the operational energy consumption of rainwater tank systems. This consumption generates a cost to the homeowner (through electricity and carbon tariffs) and to the environment through associated greenhouse gas emissions. A number of Australian and international studies have determined the energy intensity of IPRWT pumps on a theoretical basis, while a few empirical studies have also been completed. Of empirical home monitoring studies, many have been completed to determine the net system energy intensity, but not at an end-use level. This chapter covers a recently completed investigation into rain tank pump performance conducted in South-east Queensland (SEQ), Australia. The study is the first known empirical in-home evaluation of rain tank pumps at an end-use level. This evaluation incorporates water and energy data captured at high resolution from 19 homes over a 6-month period, combined with socio-economic and stock inventory data.