National Water-Quality Assessment (NAWQA) Program
932 public wells were sampled
The 932 public wells (colored circles) are located in parts of 41 states and withdraw water from parts of 30 regionally extensive aquifers used for public water supply. The colored areas on this map represent different principal aquifer rock types, each of which has different geologic characteristics.
About 105 million people—more than one-third of the Nation’s population—receive their drinking water from one of the 140,000 public water systems across the United States that use groundwater as their source.
Scientists from the U.S. Geological Survey (USGS) assessed water-quality conditions in source (untreated) groundwater from 932 public wells, and in source and finished (treated) water from a subset of 94 wells. A greater number of chemical contaminants (as many as 337), both naturally occurring and man-made, were assessed in this study than in any previous national study of public wells.
The objectives of this study were to evaluate (1) the occurrence of contaminants in source water from public wells and their potential significance to human health, (2) whether contaminants that occur in source water also occur in finished water after treatment, and (3) the occurrence and characteristics of contaminant mixtures.
Maps, Graphics, and Tables
Frequently Asked Questions
Presentation of Findings to Congress on May 21, 2010
Data (ZIP 263KB)