60 Water Testing Statistics

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These water testing figures cover the measurement periods and populations identified in the available source material. Estimates, surveys and forecasts retain their reported scope.

Key Water Testing Statistics

The main findings are:

  • The United States had 148,541 active public water systems in calendar year 2023.
  • The preliminary UCMR 5 dataset contained 100,629 analytical results from 9,539 entry points at 3,722 public water systems (through February 2024; United States participating public water systems).
  • More than 43 million people, about 15% of the U.S. population, rely on domestic private wells for drinking water (2015 population estimate cited by USGS).
  • Arsenic exceeded the 10 micrograms-per-liter EPA benchmark in about 11% of 7,580 evaluated wells (national retrospective study; United States domestic wells).
  • CDC-supported programs coordinated with state public-health and private laboratories through 11 recipients (CDC-funded program period 2015-2020; United States participating programs).
  • In 2022, 27% of the global population, or 2.2 billion people, lacked safely managed drinking water.
  • 107,559 public water systems, or 72%, had no reported drinking-water-standard violations in 2023 (United States public water systems).
  • PFOA was at or above its minimum reporting level in 1,076 of 16,772 samples, or 6.4% (through February 2024; UCMR 5 participating systems).
  • About one in five wells in a USGS study of 2,100 domestic wells had one or more contaminants above a human-health drinking-water benchmark (study period reported by USGS; United States domestic wells).
  • Nitrate exceeded the 10 milligrams-per-liter EPA benchmark in about 8% of 3,465 evaluated wells (national retrospective study; United States domestic wells).
  • The programs digitized 210,000 private-well records (CDC-funded program period 2015-2020; United States participating programs).
  • USGS Water Data for the Nation contains more than 4.4 million historical water-quality analyses through September 2005.
  • 40,982 public water systems, nearly 28% of the 2023 active total, were reported to have violated at least one drinking-water standard (United States public water systems).
  • PFOS was at or above its minimum reporting level in 1,149 of 16,768 samples, or 6.9% (through February 2024; UCMR 5 participating systems).
  • Man-made organic compounds were detected in 60% of sampled domestic wells (USGS domestic-well study; United States sampled domestic wells).

Contents

Water testing statistics for U.S. public water-system compliance

EPA annual compliance-report universe; system counts can differ with query definitions.

No reported violation is not the same as proof that every contaminant was absent.

Reported violations depend on submitted compliance and monitoring data.

Includes contaminant exceedances or treatment-technique failures as defined by EPA.

A monitoring/reporting failure means contaminant information may be late, incomplete or unreported; it is not itself a contamination result.

EPA priority status is based on violation points and duration.

This is a composition statistic for priority systems, not all small systems.

Counts reported enforcement actions, not unique contaminant tests.

Informal action count is not a count of samples or contaminant detections.

Return-to-compliance reporting does not quantify the number of tests or duration of prior noncompliance.

PFAS water testing data from UCMR 5 monitoring

The preliminary dataset represented about 24% of results expected in the final dataset.

Preliminary sample-level result; minimum-reporting-level detection is not an MCL compliance determination.

Preliminary sample-level result.

A system-level detection is not the same as a running annual average MCL violation.

Preliminary system-level detection.

Single-sample threshold exceedance; EPA states compliance is based on running annual averages, not a single sample.

Preliminary and not equivalent to final regulatory compliance.

Only complete sample sets for the six PFAS were included.

Preliminary co-occurrence analysis.

Private well water testing statistics and contamination

  • More than 43 million people, about 15% of the U.S. population, rely on domestic private wells for drinking water (2015 population estimate cited by USGS). (Domestic (Private) Supply Wells)
  • About one in five wells in a USGS study of 2,100 domestic wells had one or more contaminants above a human-health drinking-water benchmark (study period reported by USGS; United States domestic wells). (Domestic (Private) Supply Wells)
  • Man-made organic compounds were detected in 60% of sampled domestic wells (USGS domestic-well study; United States sampled domestic wells). (Domestic (Private) Supply Wells)
  • Man-made organic compounds exceeded human-health benchmarks in less than 1% of sampled domestic wells (USGS domestic-well study; United States sampled domestic wells). (Domestic (Private) Supply Wells)
  • Microbial contaminants were detected in about one-third of approximately 400 domestic wells tested for microbes (USGS domestic-well study; United States sampled domestic wells). (Domestic (Private) Supply Wells)

Population estimate is not a current well census and private wells are generally outside federal monitoring.

Study sample is not a complete random census of all private wells.

Detection does not mean the concentration exceeded a health benchmark.

Applies to the organic compounds assessed in the study.

Microbial subset was approximately 400 wells, smaller than the overall study.

What water-quality testing finds in domestic wells

Retrospective dataset was not originally designed as a statistically representative national sample.

The cited abstract does not give the uranium-specific denominator.

300 pCi/L was a potential drinking-water standard under review, not necessarily a current enforceable standard.

4,000 pCi/L was a potential standard under review in the cited study.

The source reports a less-than-1% category rather than an exact percentage.

Water sample collection and laboratory testing programs

Program output count, not a national estimate of all water laboratories.

Records were from participating jurisdictions, not all U.S. wells.

Participating-program records; record count is not a unique national well count.

Distribution is not the same as completed laboratory tests.

Program sample total, not a national surveillance estimate.

High level is program-defined; the page does not state one common contaminant threshold for every sample.

People-served estimate relates to the program’s affected samples, not a national exposure estimate.

Local program result, not representative of North Carolina or the United States overall.

Selected-community program count, not a statewide estimate.

Participation measure, not a water-quality outcome.

Weighted survey estimates; source describes drinking-water source, not water-test results.

Weighted survey estimates and historical period.

Self-reported historical testing, not verified laboratory records.

Self-reported survey measure.

Recall-based and does not identify contaminant, concentration or health significance.

Global drinking-water quality statistics and data coverage

Safely managed means water at home, available when needed and safe; this is a modeled/compiled service indicator, not a household test rate.

The cited database compilation cutoff is historical and includes varied projects and sample types.

Site inventory includes water, biological tissue, sediment and other environmental samples, not drinking-water tests only.

Current-condition measurements can include provisional data subject to revision.

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