In 1990, the last time the decennial census included a question on domestic drinking water source, it was estimated that private domestic water wells (PDWs) supplied household water to about 15.1 million housing units (15% of the population) in the United States (U.S.). PDWs are not regulated by the Safe Drinking Water Act, and with few exceptions, are not subject to the water quality testing required of public water suppliers. We expanded two methods in estimating housing units reliant on PDWs from an Oklahoma pilot study (Weaver et al. 2017), nationally. Both use 1990 census data on drinking water sources as a baseline. The first method uses housing unit change and private well drilling logs for 20 states. This allows for the rate of well use to change between 1990 and 2010 in these states. The second, based solely on housing unit change, assumes a constant rate of well use. Ordinary least squares regression demonstrated (R 2 = 0.78) that the methods yield similar estimates for nationwide well use. Using the housing unit change method, it is estimated that in 2010, 23 million housing units were reliant on PDWs (17% of the population). We provide these estimates at the census block group and census block resolution. This dataset will assist in a better understanding of the reliance on PDWs in the U.S., and position local, tribal, state, and national groups to better protect this water resource from contaminant sources.
Research impact statement: The work provides improved estimates of the spatial distribution of housing units reliant on private domestic wells in the United States and a foundation to protect this water supply at all levels of government.
Keywords: GIS; dasymetric; drinking water; geospatial analysis; private domestic wells.