More than 20 percent of untreated water samples from 932 public wells across the nation contained at least one contaminant at levels of potential health concern, according to a new study by the U.S. Geological Survey (USGS).
But most of these contaminants are naturally occurring, the USGS found. Naturally occurring contaminants, such as radon and arsenic, accounted for about three-quarters of contaminant concentrations greater than human-health benchmarks in untreated source water. Naturally occurring contaminants are mostly derived from the natural geologic materials that make up the aquifers from which well water is withdrawn.
Man-made contaminants were also found in untreated water sampled from the public wells, including herbicides, insecticides, solvents, disinfection by-products, nitrate, and gasoline chemicals. Man-made contaminants accounted for about one-quarter of contaminant concentrations greater than human-health benchmarks, but were detected in 64 percent of the samples, predominantly in samples from unconfined aquifers.
The USGS study focused primarily on source (untreated) water collected from public wells before treatment or blending rather than the finished (treated) drinking water that water utilities deliver to their customers.
This study and additional information about public wells can be found on the Quality of Water from Public-Supply Wells in the United States website.
People served by public water systems can obtain information about their drinking-water quality from their water supplier. Selected water suppliers provide an annual water-quality report; some reports are available on EPA's Consumer Confidence Reports (CRR) website.
Companion USGS studies on the transport of contaminants to public supply wells are online. In addition, a comparable study on the quality of water in domestic wells is online.
