Connecticut Water Quality by ZIP Code — Open Dataset

The per-ZIP contaminant data behind CheckYourTap, published as a free, open dataset. Contaminant detection and health-guideline exceedance rates for 300 Connecticut ZIP codes, from EPA and Connecticut state public water system testing.

What's in it

One row per ZIP code + contaminant, with columns: zip, town,state, contaminant, slug, detection_pct,exceedance_pct, denominator, limit, safety_class, and enforceable. Public (city) water systems only — private wells are not included.

Read the denominator column before you use a percentage. It is not the same for every row, and averaging across it will give you a wrong answer. Lead and copper come from the Lead and Copper Rule, and PFAS and chromium-6 from the UCMR rounds; both programmes report every sample, so for those rows detection_pct is a real share of all samples tested. For the rest, the EPA records we draw on keep only the samples in which something was found, so no detection rate exists (detection_pct is null) and the exceedance rate is a share of the detections alone.

Provenance: some ZIP codes share one regional water system (for example, several lower-Fairfield-County towns are served by the Aquarion regional system), so their results are identical. The data is per public water system as it maps to each ZIP — not always independently sampled per ZIP.

License & citation

Released under CC-BY 4.0 — free to use, including commercially, with attribution to CheckYourTap (checkyourtap.com). Suggested citation: “Connecticut Public Drinking-Water Quality by ZIP Code,” CheckYourTap (Valiant Energy Solutions), checkyourtap.com/data. See CITATION.cff.

Want your own address instead of the raw data? Check your ZIP for a personalized report.