A unit of water that measures the volume of water used by a household each day. Generally, this is calculated for a community water service, city, county, or state and reflects monthly volume of water used divided by the number of households in that community and divided by 30 days in an average month. This provides an average estimate of household water use and serves as a benchmark to measure changes in water use over time. GPHD is sometimes preferred to “per capita” or “per-person” units because water is typically purchased and used by entire households rather than by individuals.