Well Water Contaminants

Illustration: a magnifying glass over a water sample with particles

Each guide explains where the contaminant comes from, why it matters, how to test for it, and what the official limits and treatment options are, with links to the EPA, CDC and state sources behind every figure.

Health-related contaminants – Coliform and E. coli in Well Water: What a Positive Test Means – Nitrates in Well Water: Health Risks, Limits and Fixes – Arsenic in Well Water: Where It Comes From and How to Remove It – Lead in Well Water: Testing Your Pipes, Pump and Fixtures – PFAS in Private Wells: Testing and Treatment – Radon in Well Water: Should You Test?

Nuisance problems (stains, scale, taste and smell) – Hard Water, Iron and Manganese in Wells: Stains, Smells and Fixes – Well Water Smells Like Rotten Eggs? Causes and Fixes for Sulfur Odor

If a test shows E. coli, or nitrate above the EPA limit, stop drinking the water, use bottled water, and contact your state or local health department.

Not sure what you have? Start with what to test your well water for, then read your results.

General information, not medical advice. Limits are from the EPA’s National Primary Drinking Water Regulations. Rules for some contaminants (such as PFAS and lead) are changing, so check each page’s “last checked” date.

All contaminants guides

Illustration: a magnifying glass over a water sample with particlesContaminantsColiform and E. coli in Well WaterTotal coliform or E. coli in your well test? What each result means, what CDC says to do next, why shock chlorination…Illustration: large water dropsContaminantsNitrates in Well WaterEPA's nitrate limit is 10 mg/L (as nitrogen). Learn why infants are most at risk, when to test, why boiling makes it…Illustration: a magnifying glass over a water sample with particlesContaminantsArsenic in Well WaterArsenic in private wells usually comes from natural rock. Learn EPA's 10 µg/L limit, who's at risk, how to test, and which…Illustration: large water dropsContaminantsLead in Well WaterIn private wells, lead usually comes from plumbing, fixtures or pump parts, not the aquifer. How corrosive water causes it, how to…Illustration: a magnifying glass over a water sample with particlesContaminantsPFAS in Private WellsPFAS ('forever chemicals') in private wells: current EPA limits and proposed changes, who should test, and how to choose a filter certified…Illustration: a farmhouse in the countrysideContaminantsRadon in Well WaterRadon from well water escapes into indoor air when you shower and wash. Who should test, the levels states use, and how…Illustration: water filter cartridges on a supply lineContaminantsHard Water, Iron and Manganese in WellsOrange stains, black specks or crusty faucets? How to read hardness, iron and manganese results for a well, EPA reference levels, and…Illustration: large water dropsContaminantsWell Water Smells Like Rotten Eggs?A rotten egg or sulfur smell in well water usually means hydrogen sulfide. How to tell if the cause is your well…