Download the data

Everything the site publishes, one CSV per state. The rollups behind every county and town page, and the state survey summaries and model estimates, as they stand today. Use them for a story, a class, a town meeting or your own map.

License: Creative Commons Attribution 4.0. Credit Well Water Nerd with a link, and the original agencies named in the source column. The underlying records are public data from the USGS Water Quality Portal and the state programs listed on each page. 5,000 measured county and town pages, refreshed 2026-09-22.

Files by state

What the columns mean

Rollups

One row per place and contaminant. A sample counts toward its town, its county and its state. Non-detects count as samples and as zero for the median. Shares are percentages. A limit_kind of epa_mcl is the enforceable federal limit; health_advisory and secondary_standard are guidance and taste levels, and the share above them is left blank.

level, fips, name, county, state, contaminant, unit, samples, wells, detected_pct, above_limit_pct, limit, limit_kind, median, p90, max, first_sampled, last_sampled, updated

Surveys and estimates

Summaries published by a state program, such as homeowner test results by town, with the share above that state's guidance level, plus the USGS national model estimate where it exists. The kind column says which.

level, fips, name, state, contaminant, kind, wells_tested, above_pct, guidance_value, guidance_unit, guidance_label, median, p95, max, period_start, period_end, source, source_url