Contaminant explainers
Short, sourced explainers. Federal limits apply to public water systems, not private wells.
Pick a contaminant
Nitrate in well water
Comes from fertilizer, septic systems and manure. Most serious for infants under six months.
Read the explainer 2266 listings test for it 0MCLG for total coliformsColiform bacteria and E. coli
An indicator test. A positive result means surface water or waste may be reaching the well.
Read the explainer 838 listings test for it 0.010mg/L (10 ppb, EPA MCL)Arsenic in well water
Often natural, from rock and soil. You can't taste it, so only a lab test will tell you.
Read the explainer 986 listings test for it 15µg/L (ppb) EPA action level, public systemsLead in well water
Mostly comes from household plumbing, not the aquifer. No known safe level in a child's blood.
Read the explainer 558 listings test for it 4.0ng/L (ppt) EPA MCL for PFOA and PFOS, public systemsPFAS in well water
Man-made 'forever chemicals'. EPA sets limits for public systems only and gives no standard for private wells.
Read the explainer 425 listings test for it 30µg/L EPA MCL, public systemsUranium in well water
Occurs naturally in some rock and soil. Kidney effects are the main concern at high levels.
Read the explainer 58 listings test for it 4pCi/L in indoor air: EPA's level to fix a homeRadon in well water
A gas from rock and soil. In most homes the air is the larger risk, and water is the second thing to check.
Read the explainer 569 listings test for it 0.05mg/L EPA secondary (aesthetic) standardManganese in well water
Stains and tastes bad at low levels. EPA also publishes health advisory values, with extra caution for infants.
Read the explainer 516 listings test for it 0.005mg/L (5 µg/L) EPA MCL for benzene, TCE, PCE; public systemsVOCs (solvents, fuel compounds) in well water
Industrial solvents and fuel-related compounds. Rare in most wells, but worth a test near sources.
Read the explainer ExplainerCopper in well water: why it comes from your pipes, what 1.3 mg/L means, and how to test it
On a private well, copper almost always comes from the plumbing, and corrosive water or new copper pipe decides how much. A first-draw and a flushed sample from the same faucet show whether running the water is enough or the water itself needs treating.
Read the explainer ExplainerE. coli in well water: what a positive means and what to do today
An E. coli positive means human or animal waste is reaching your well. Here is the household checklist for today, the people who need a doctor's advice, how to trace the source this week, and the retest schedule state and federal agencies give.
Read the explainer ExplainerFluoride in well water: the two federal limits, how to test, and what your number means for children
Most U.S. domestic wells have less fluoride than the 0.7 mg/L dental benchmark, and a few have more than EPA's 2.0 and 4.0 mg/L levels. One lab test tells you which, and your child's dentist needs that number either way.
Read the explainer ExplainerSalt in well water: sodium, chloride and sulfate, where they come from and what the numbers mean
"Salt" on a well report is three results: sodium, chloride and sulfate. Each has its own EPA guideline, none enforceable on a private well, and each points to different sources, from road salt and softeners to seawater and rock.
Read the explainer ExplainerSediment in well water: what sand, silt or mud means, and when it calls for a bacteria test
Most grit in well water is a nuisance that points to the well, the pump or the water's chemistry. Water that turns muddy after heavy rain is different: it can mean surface water is getting in, so test for coliform bacteria first.
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