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The team found surface water accounted for 81% of the water supply for a typical large city and 100% of the supply for more than half of the large cities studied.

A comparison of more than 100 large US cities showed pollution from point and nonpoint sources

Too often, surveys of water quality in the United States have been regionally inconsistent patchworks that neglect many unregulated contaminants.

A granular study of potential source water contamination in the largest cities in the U.S. has been lacking. New research in the journal Nature, however, shows drinking water supplies in major cities are potentially contaminated by human activities both within municipal boundaries and in the outlying watersheds on which they rely.

Legacy Water Problems

When most centralized water systems were built, the water bodies they tapped were pristine. In the 21st century, however, land use is much more widespread throughout watersheds and virtually none of the nation’s surface water is drinkable without treatment.

Every year in the U.S., drinking-water health violations affect as many as 45 million residents.

  • Nitrates from agricultural runoff increasingly contaminate drinking water for millions.
  • PFAS chemicals that leach from airports, oil refineries, military installations, and industrial operations are elevated for 6 million citizens.
  • Treated wastewater finds its way into half of the nation’s municipal drinking water treatment plants, bringing the risk of exposure to cryptosporidium, norovirus, pharmaceuticals, and endocrine disrupting compounds (EDC) along with it.

But not enough data is available to compare potential source water contamination between cities. The Clean Water Act provides guidelines, but each state uses its own methodology, making a national comparison difficult.  National Aquatic Resource Surveys do not focus on important emerging contaminants. To complicate matters, major cities often withdraw and blend water from many intakes, both close to home and in remote regions, and the researchers have found wide variation in the relative contaminant contributions of point and nonpoint sources of pollution.

Developing a New Dataset

The study integrated nationwide geospatial datasets with hydrologic simulations to estimate water supply contamination for 116 of the largest cities in the U.S. All of the cities studied have populations of more than 150,000, and, taken together, account for approximately a quarter of the national population.

The team first combined spatially referenced drinking water catchments with geospatial layers of human activities to gauge potential contamination in the cities’ water supplies. They looked at public data from water utilities and determined the cities’ multiple water sources and the respective contributions they make to total each municipal supply. The researchers derived two metrics from the resulting citywide breakdowns: the proportions of potentially contaminated supply (PPCS) for both point and nonpoint sources.


The team found surface water accounted for 81% of the water supply for a typical large city and 100% of the supply for more than half of the large cities studied. A surprising 80% of cities that rely on surface water deliver treated wastewater to their utility customers in what amounts to unplanned wastewater reuse, along with its attendant risks. And 5% of the cities’ drinking water supplies rely primarily on runoff from questionable areas, including farms, residential neighborhoods, and industrial areas.

The team hopes their exposure-based PPCS metrics will have value as a tool to infer actual source drinking water contamination risk.

The Decentralization Solution

Moving forward from the centralized treatment mindset of the past, Fluence manufactures a number of decentralized solutions to tackle problems across watersheds with both point-source treatment and drinking water purification technologies. Over a wide region with multiple sources of potential contamination, it’s much more efficient to treat on-site rather than construct pipelines to distant central plants.

While much of the contamination examined in the study comes from nonpoint sources, the legal definition of a point source seems to be evolving. The National Oceanic and Atmospheric Administration (NOAA) describes even a feature as small as a ditch as a possible point source.

For example, Fluence’s Aspiral™ wastewater treatment plants — which feature very high nutrient removal — can solve point-source nitrate pollution problems at the source. And modular NIROBOX™ plants can be configured to treat various water sources and produce drinking water quality. Both are packaged in standard shipping containers for easy transportation and installation, even in remote areas.

Whether water managers prefer to address the problems highlighted by the study through watershed restoration or through drinking water purification, decentralized treatment can bring treatment directly where it’s needed without miles of unneccesary pipeline. Contact the experts at Fluence to discuss mature technologies and proven decentralized strategies to address your challenges.

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