Abstract: The national demand for water in the UK is predicted to increase, exacerbated by a growing UK population, and home-grown demands for energy and food. When set against the context of overstretched existing supply sources vulnerable to droughts, particularly in the SE of the UK, the delicate balance of matching minimal demands with resource secure supplies becomes critical. Whilst demands can be decreased through changes in user behaviour and adoption of technological efficiency and supplies can be supplemented with additional local sources (e.g. rainwater harvesting – RWH and greywater – GW), careful consideration of future water use performance, particularly in increasingly dense city centres needs to be considered. For this purpose indicators and benchmarks are particularly useful, although any system, once adopted, must be robust and fully understood in terms of its sensitivity to future changes. This paper presents a new benchmarking system for measuring the water using performance of domestic dwellings and considers the impact(s) therein when making changes to ‘internal’ demands either through technological efficiency or user behaviour alone. The sensitivity of water performance is then tested further when combining these changes with additional localised supplies (i.e. RWH and GW) and ‘external’ gardening demands. Therein the impacts (in isolation and combination) of the following are considered: occupancy rates (1 to 4); roof size (12.5 m² to 100m²); garden size (25 m² to 100m²); geographical location (NW, Midlands, SE) and yearly temporal effects. Lessons learnt from analysis of the proposed benchmarking system are made throughout this paper, in particular its compatibility with the existing code for sustainable homes accreditation system. Conclusions are subsequently drawn for the robustness of the proposed system.