Drinking water violations

Change in measure calculation in 2018: Drinking Water Violations is an indicator of the presence or absence of health-based drinking water violations in counties served by community water systems. Health-based violations include Maximum Contaminant Level, Maximum Residual Disinfectant Level and Treatment Technique violations. A "Yes" indicates that at least one community water system in the county received a violation during the specified time frame, while a "No" indicates that there were no health-based drinking water violations in any community water system in the county. Please note that the methods for calculating this measure changed in the 2016 Rankings.

Measure Tabs

Reason for Ranking

Recent studies estimate that contaminants in drinking water sicken 1.1 million people each year. Ensuring the safety of drinking water is important to prevent illness, birth defects, and death for those with compromised immune systems. A number of other health problems have been associated with contaminated water, including nausea, lung and skin irritation, cancer, kidney, liver, and nervous system damage.

Measurement Strengths and Limitations

There are a number of limitations associated with this measure: 

  • The number of violations within each system is not taken into account, and estimates are not available for the number of people who consume infected water or get ill from consumption.
  • Not all violations are equivalent; some violations occur but are addressed quickly, while some violations can linger for years. Violations could be slightly over or much higher than the MCL. 
  • Testing date, frequency, location, and type can play a role in violation detection.
  • This measure only includes data on community water systems, and does not include private wells.
  • The required reporting of water quality tests is often based on annual and/or system-wide averages of individual sampling results. For example, Community Water Systems (CWS) may be required to sample at four different locations, but report only the average.
  • What violations are labeled as health based have changed over time.