Australia, as an arid continent with Western consumption habits, is particularly susceptible to potable water scarcity. The extended periods of drought experienced by the majority of the nation from 2000-2009 led to the introduction of legislation mandating that all new residential dwellings achieve potable savings targets. Internally plumbed rainwater tanks are the most widely used means of satisfying these requirements. The least transparent variable affecting the viability of these decentralised supply systems is the pump energy and its associated costs. However little research has investigated what these costs are for specific end-use events (e.g. cistern flush). This paper reveals the pump energy intensity for a variety of end-uses under common system configurations. The experimental design consisted of three high resolution water meters and an electricity meter installed in each home collecting data at 5-second intervals before transmitting wirelessly to servers over cellular networks. Once combined with relevant socio-demographic data, water and energy usage was disaggregated into individual end-use events, even when events were occurring simultaneously or when supply was split between sources. Findings determined that for the mandated rain tank enduses, cistern half-flushes are the most energy intense, followed by cistern full-flushes and clothes washer events, while irrigation events are significantly more efficient. Minimisation of pump energy, whilst maintaining potable savings, acts to lower electricity costs and GHG emissions. This information has broader implications in the evaluation and optimisation of internally plumbed rainwater tanks amid the spectrum of alternate urban water supply systems.