Who Gets Tap Water from Underground? Mapping America’s Public-Supply Groundwater

Turn on a kitchen faucet and the water may have traveled from a river, a reservoir, or a well drilled into layers of sand, gravel, limestone, or fractured rock. That hidden geography matters: it shapes which communities depend on which aquifers, which water sources need protection, and who may be affected when drought, contamination, or growth puts pressure on groundwater.In this episode, we unpack a national USGS mapping study that asks a deceptively simple question: where are the people who get public drinking water from groundwater, and which underground water-bearing regions supply them? The team combined census data, public water-use records, land-use maps, and tens of thousands of public-supply well records to build a high-resolution picture of public-supply groundwater in the conterminous United States in 2010.The headline numbers are striking but practical: about 269 million people used public-supply water; about 107 million of them were supplied by groundwater and about 162 million by surface water. When private-well users are included, the study estimates that roughly 144 million people—about 47% of the conterminous U.S. population in 2010—relied on groundwater. The episode explains how the researchers mapped people to places, why they created 177 hydrogeologic mapping units, and what it means that stacked aquifers can supply the same community from different depths.Citation: Johnson, T.D., Belitz, K., Kauffman, L.J., Watson, E., & Wilson, J.T. (2022). Populations using public-supply groundwater in the conterminous U.S. 2010; Identifying the wells, hydrogeologic regions, and hydrogeologic mapping units. Science of the Total Environment, 806, 150618. https://doi.org/10.1016/j.scitotenv.2021.150618Disclosure: This Waterlines episode uses AI-generated voices for the hosts. The scientific discussion is based on the cited paper and is written for public understanding, not as a substitute for local water-system guidance.