Current water supply worldwide is facing growing pressure as a result of climate change and increasing water demand due to growing population and lifestyle changes. The traditional way of fulfilling the growing demand–supply gap by seeking new water supply options such as exploiting new fresh water resources and investing in the expansion of infrastructure is no longer considered environmentally or economically sustainable. A diverse portfolio of water efficiency measures is now a requirement for the majority of water companies in the UK. This paper presents results from a statistical analysis of a unique water efficiency program case study. The study evaluates the effectiveness of installing water-saving devices in single-family households in areas where a major UK water supply company operates. Using multilevel models, the study accurately measures the water savings achieved through the efficiency program and defines the factors that affect a household's potential to save water. Analysis illustrated a mean 7% decrease in consumption, explicitly attributable to the efficiency program. Research findings provide strong evidence that single resident and financially stretched households have a bigger potential to conserve water than larger and more affluent ones and also highlight the robustness of multilevel analysis, even in cases of data limitations.