Water Quality

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Drinking Water

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Drinking water quality in 2020 was slightly lower with chloride again being the most common contaminant detected in public water systems.

This indicator shows the percentage of the population served by Community Water systems and Non-Transient Non-Community Water systems that demonstrated full compliance with applicable standards, after weighting the reports to account for the number of people served by each system. Though long-term problems occur, they are rare in large systems. 

Data for 2020 show an increase in the number of violations, based on the number of people served, from 2019 levels.35  By far, the most common problem during 2020 in water systems was excessive levels of chloride,** which is typical of most years. In addition, the Connecticut Department of Public Health (DPH) oversees the monitoring for lead by public water supplies, and also requires public water to be tested for corrosive properties (including pH) that might result in lead contamination. 

A 2019 report by the Auditors of Public Accounts for calendar year 2017 recommended that the DPH strengthen oversight and enforcement. A 2020 update indicated that DPH implemented seven of the Auditor’s recommendations, and was still working on addressing the other ten recommendations identified in the 2019 Audit Report.

About 80 percent of people in Connecticut are supplied by the public water systems included in the chart above. The remainder of the population relies on private wells, which are not monitored by any government agency and are not counted in this indicator. An unknown but significant number of private wells are contaminated by pollution or naturally occurring toxins, such as arsenic and uranium. A recent United State Geological Survey study of groundwater samples collected from more than 2,000 private wells in bedrock aquifers in Connecticut found that 3.9 percent of collected samples contained arsenic concentrations greater than the U.S. Environmental Protection Agency’s (EPA) maximum contaminant level (MCL) of 10 micrograms per liter (µg/L), and 4.7 percent of collected samples contained uranium concentrations greater than the EPA MCL of 30 µg/L.36  The DPH provides guidelines for testing of private wells.


Goal: It is assumed that the goal is for everyone to have safe drinking water.

Technical Notes: *The vertical axis in the chart above has been shortened, beginning at 90 percent rather than the customary zero. This allows the reader to see year-to-year differences, which would be nearly imperceptible if the chart began at zero. **The standard for chloride is set by state regulation.


35 Department of Public Health, Drinking Water Section; personal communication from C. Roy, February 22, 2021.
36 United States Geological Survey, “Arsenic and Uranium Occurrence in Private Wells in Connecticut, 2013–18— A Spatially Weighted and Bedrock Geology Assessment”; Eliza L. Gross and Craig J. Brown, Open-File Report 2020–1111. Version 1.1, November 2020.