Water heating is an important end-use, accounting for roughly 16% of total primary energy consumption in the US residential sector. Recently enacted efficiency standards on water heaters and hot water-using equipment (e.g., dishwashers, clothes washers, showerheads, and faucets) will substantially affect the energy use of water heaters in the future. Assessment of current and future utility programs and government policies requires that regulators, resource planners, and forecasters understand the effects of these regulations. In order to quantify these impacts, this paper presents a detailed end-use breakdown of household hot and cold water use developed for the US Department of Energy. This breakdown is based on both previous studies and new data and analysis. It is implemented in a spreadsheet forecasting framework, which allows significant flexibility in specifying end-use demands and linkages between water heaters and hot water-using appliances. We disaggregate total hot and cold water use (gallons per day) into their component parts: showers, baths, faucets (flow dominated and volume dominated), toilets, landscaping/other, dishwashers, and clotheswashers. We then use the end-use breakdown and data on equipment characteristics to assess the impacts of current efficiency standards on hot water use and water heater energy consumption.