Uses of a long-term water production database

Water suppliers must plan ways to meet expected future urban water needs associated with population increases. Examining historical urban water use data is one way to help evaluate the future. This article reviews long-term data on urban water production throughout California and illustrates how different factors affect water production. California is the nation's most populous state and currently is home to one of every eight US residents. It also provides a varied cross-section of water use conditions. The US Census Bureau forecasts that the nation's population will reach 325 million in 2020, some 46 million of whom are expected to live in California. California has exhibited a consistent trend in population growth over time, and the California Department of Finance expects this trend to continue in the future (Figure I). Historically, the nation's population growth has been accompanied by demographic trends resulting in greater urbanization of the population. Over the past century, for example, major demographic trends have included a shift in population from the eastern United States to the western United States. This trend has resulted in a net depopulation of areas such as the northern Great Plains states and a reduction in on-farm populations. Populations have been increasingly concentrated in large metropolitan areas, their suburbs, and exurban rings around the suburbs. In turn, public water systems serve increasingly larger segments of the total population (Case & Alward, 1997). The US Geological Survey (USGS) estimates that public water suppliers served about 84% of the total US population in 1995, up 7% from 1990 levels (Solley et al, 1998).