Comparison of potential drinking water source contamination across one hundred US cities

In the U.S. today nearly no surface waters are drinkable without treatment. Here, the authors demonstrate that four-fifths of cities that withdraw surface water are supplying water that includes a portion of treated wastewater, concentrated in the Midwest, the South, and Texas. Drinking water supplies of cities are exposed to potential contamination arising from land use and other anthropogenic activities in local and distal source watersheds. Because water quality sampling surveys are often piecemeal, regionally inconsistent, and incomplete with respect to unregulated contaminants, the United States lacks a detailed comparison of potential source water contamination across all of its large cities. Here we combine national-scale geospatial datasets with hydrologic simulations to compute two metrics representing potential contamination of water supplies from point and nonpoint sources for over a hundred U.S. cities. We reveal enormous diversity in anthropogenic activities across watersheds with corresponding disparities in the potential contamination of drinking water supplies to cities. Approximately 5% of large cities rely on water that is composed primarily of runoff from non-pristine lands (e.g., agriculture, residential, industrial), while four-fifths of all large cities that withdraw surface water are exposed to treated wastewater in their supplies.

Automated summary

In the U.S., most cities rely on surface water sources that include treated wastewater, with concentrations in the Midwest, South, and Texas. Potential contamination of drinking water supplies from local and distal source watersheds is a concern, as water quality sampling surveys are often inconsistent and incomplete. The diversity of anthropogenic activities across watersheds leads to disparities in potential contamination of drinking water supplies for large cities.