Well Water Testing: What to Test For and How Often

If your water comes from a private well, nobody tests it unless you do. There’s no utility, no annual report and no legal limit that applies to your tap.

Short answer: test your well at least once a year for total coliform bacteria, nitrate, total dissolved solids (TDS) and pH, the core panel both the CDC and the EPA recommend. Add tests for what’s likely in your area (arsenic, radon, uranium, PFAS, pesticides, fuel compounds and so on), and test again right away after a flood, a well repair, or any change in taste, color or smell. Use a state-certified lab, follow its sampling instructions, and compare the results with EPA drinking water standards.

In practice that’s one sample kit a year for most households, plus a broader panel once and whenever something changes.

Is private well water regulated by the EPA?

No. According to the EPA, “the quality and safety of drinking water from private domestic wells are not regulated by the Federal Government,” and most states don’t regulate them either (EPA, Private Drinking Water Wells). The same page puts the number of people who rely on private wells at around 15% of the US population, over 43 million.

In the EPA’s words, “Private well owners are responsible for delivering safe drinking water to their households.” Federal limits for nitrate, arsenic, PFAS and the rest are written for public water systems. They’re still the best yardstick for your well, but no one enforces them on it.

On city water, your utility tests for you and publishes the results each year: start with how to read your water quality report instead.

Are private wells usually contaminated?

Most aren’t, but enough are that testing is worth it. The largest national look is a US Geological Survey study of about 2,100 domestic wells in 48 states, sampled from 1991 to 2004 (USGS Circular 1332). It found that 23%, more than one in five, had at least one contaminant above a human-health benchmark.

Two details matter for how you test:

• Most problems were natural. The contaminants most often above benchmarks were inorganic chemicals, and all but nitrate came mainly from natural sources. Your well can have them even if nothing nearby has ever been polluted.
• No single contaminant was common. The full USGS report found none above a benchmark in more than 8% of wells: nitrate, arsenic and manganese each in about 5 to 7%, fluoride and uranium in about 1 to 2%. (Radon was higher, but only against limits that were proposed and never finalized.) What you need to test depends on where you live.

The benchmarks were EPA limits for public systems or USGS health-based screening levels, and the sampling is more than 20 years old, so read it as a picture of the problem, not current rates.

What should you test your well water for every year?

The CDC’s guidelines for testing well water say to test “at least once each year” for:

• Total coliform bacteria. Coliforms are mostly harmless themselves, but they’re an indicator: if the count is high, the CDC says harmful germs may also be present. A positive for fecal coliforms or E. coli likely means feces have reached your well.
• Nitrate. It comes from fertilizer, septic systems and animal waste. The CDC says all well owners should test for it each year, because high levels can make people sick, especially babies.
• Total dissolved solids (TDS). A general measure of minerals and salts in the water.
• pH. How acidic or alkaline the water is, which affects corrosion of pipes and fixtures.

The EPA’s guidance for well owners lists the same four, and adds that you should test more often if small children or older adults live with you, or if someone in the house is pregnant or nursing.

States may set their own schedule. The Minnesota Department of Health, for example, recommends coliform bacteria every year, nitrate every other year, and arsenic and lead at least once. Your state’s well program knows the local risks best.

What else should you test for, depending on where you live?

The CDC says the right tests depend on where the well sits on your property, your state or region, and whether you live in a rural or urban area. It suggests asking your local health or environmental department, or calling the EPA’s Safe Drinking Water Hotline at (800) 426-4791.

Natural contaminants from local geology

• Arsenic. A USGS and CDC team used arsenic results from 20,450 domestic wells to model the chance of a well exceeding 10 µg/L, the EPA limit for public systems (Ayotte et al., 2017). They estimated that about 2.1 million people in the lower 48 states (95% confidence interval 1.5 to 2.9 million) drink from wells above that level. It’s a model with data gaps in some regions, built for broad screening, not a prediction for your well. But it’s the clearest reason to test for arsenic at least once.
• Radon. A naturally radioactive gas. The EPA recommends that well owners test their drinking water for it, and its own testing table says to test for radon if radon shows up in your indoor air or your region is radon-rich. Most of the risk is from breathing it: the EPA’s older radon page attributes about 89% of the estimated cancer deaths from radon in water to radon released into indoor air, and 11% to drinking it (EPA, radon in drinking water).
• Uranium and other radionuclides. The EPA lists naturally occurring deposits, along with uranium and coal mining, as sources that can reach private wells (EPA, potential well contaminants). Ask your state whether they’re common where you live.
• Iron, manganese and hydrogen sulfide. The EPA links stained fixtures and laundry to iron and manganese, and an objectionable taste or smell to hydrogen sulfide. Iron is mainly a stain and taste issue; manganese also has a health benchmark in the USGS work above. Test before you buy any treatment.

Contaminants from activity nearby

The EPA’s well owner page matches what’s around you with what to test:

If you have…	Test for
Intensive agriculture nearby	Nitrate, nitrite, pesticides, coliform bacteria
Coal or other mining nearby	Metals, pH, corrosion
Gas drilling nearby	Chloride, sodium, barium, strontium
A dump, junkyard, landfill, factory, gas station or dry cleaner nearby	Volatile organic compounds, TDS, pH, sulfate, chloride, metals
A gasoline or fuel oil smell, or buried fuel tanks nearby	Volatile organic compounds
Lead in your plumbing or service line, or corroding pipes	pH, lead, copper
Stained fixtures or laundry	Iron, copper, manganese
A salty taste, seawater or a heavily salted road nearby	Chloride, TDS, sodium
Scaly residue, soap that won’t lather	Hardness
Recurring stomach illness in the household	Coliform bacteria

The EPA notes that not everything on this list is a health risk: some only affect taste, smell or appearance, like hardness (see hard water). Lead can come from your plumbing as well as the ground: see lead in drinking water.

PFAS

PFAS aren’t on the CDC’s basic list, but they do turn up in wells. In a USGS survey of tap water at 716 locations across the US (269 private wells and 447 public supplies, sampled 2016 to 2021), PFAS levels and mixes were broadly similar in private wells and public supplies, and the authors estimated at least one PFAS could be detected in about 45% of US drinking-water samples (Smalling et al., 2023). Detection varied a lot by place, and the study measured exposure, not health effects.

Nearby potential sources and land use were related to how much PFAS showed up, so a PFAS test makes most sense if there’s a likely source near your well or your state has found PFAS in local wells. Our PFAS guide covers what the levels mean.

When should you test well water beyond the yearly test?

The CDC and EPA list these triggers. Test promptly if:

• you’re told there are well water problems in your area;
• there’s flooding, land disturbance, new construction, industrial activity or a waste site near your well;
• you replace or repair any part of the well system;
• your water’s taste, color or smell changes;
• someone in your home becomes pregnant, or a child (especially a new baby) comes to live with you.

After a flood, the CDC’s advice is to drink bottled water until you’re sure the well is free of contaminants, or to boil it (a rolling boil for 1 minute) until it’s been tested (CDC, disinfecting wells after an emergency). It recommends that a well or pump contractor disinfect the well, and that you wait at least 7 to 10 days after disinfection, once all the chlorine is flushed out, before testing again. If the water smells of fuel or chemicals, boiling and disinfection won’t make it safe: use bottled water and call your local health department.

With a baby in the house, nitrate is the test that matters most. The EPA says infants under six months who drink water with nitrate above the limit can become seriously ill. If you’re preparing formula with well water, get a recent nitrate result and ask your pediatrician or health department how to use it.

How do you find a state-certified lab?

Both the CDC and the EPA say to use a state-certified laboratory. The EPA keeps a list of each state’s lab certification program, where you can look up certified labs near you (EPA, certified drinking water labs). The EPA itself can’t test residential water on request.

Start with your county or state health department. The CDC says it should have a list of certified labs, and the EPA notes that some local health departments test private wells for free. Minnesota’s guide, for one, suggests asking your county whether it offers well water testing.

Confirm the lab is certified for each test you order, and get its bottles and instructions before you sample. Home test strips can give a quick look at things like hardness, but for results you act on, the EPA’s advice is to “only use laboratories that are certified to do drinking water testing.”

How do you take a well water sample?

Follow your lab’s instructions to the letter: holding times, bottles and preparation differ between tests and labs. As an example of what good technique looks like, the Wisconsin DNR’s coliform sampling guide (written for public systems, but the same idea) asks samplers to:

1. Wash your hands with soap and water, and label the bottle in waterproof ink.
2. Use a clean cold-water faucet that doesn’t leak, with no swivel or mixing valve if possible, and remove the aerator, gasket and any other attachments.
3. Run the water long enough to flush the pipes (its guide says a minimum of 5 to 30 minutes, longer for long pipe runs), then turn it down to a steady, thin stream.
4. Open the bottle without touching its mouth or the inside of the cap. Don’t rinse it: any powder inside is there on purpose, to neutralize chlorine.
5. Fill to the fill line, cap it tightly, keep it cold and get it to the lab fast. Its bacteria samples must be analyzed within 30 hours of collection.

If you have a softener or filter, ask the lab whether to sample before it, after it or both. And don’t sample right after the well has been disinfected: the CDC says to wait until all the chlorine is flushed out.

How do you read your well water test results?

Your report should give a concentration for each substance, and many labs flag anything above an EPA standard. If yours doesn’t, the EPA suggests comparing it with its list of maximum contaminant levels (MCLs). Watch the units: mg/L is the same as parts per million (ppm), and µg/L is parts per billion (ppb).

Here are the common ones, as of October 2026. These are legal limits for public water systems; for your well they’re reference points.

Test	EPA number	What kind of number
Total coliform / E. coli	Goal of zero	Legal rule for public systems; for a home well, aim for “absent”
Nitrate (as N)	10 mg/L	Legal limit (MCL)
Nitrite (as N)	1 mg/L	Legal limit (MCL)
Arsenic	0.010 mg/L (10 µg/L)	Legal limit (MCL)
Uranium	30 µg/L	Legal limit (MCL)
Fluoride	4.0 mg/L	Legal limit (MCL)
PFOA, PFOS	4.0 ng/L (ppt) each	Final 2024 limits; compliance due 2029, with a proposed option to extend to 2031
Radon	No federal limit	300 and 4,000 pCi/L were proposed in 1999; never finalized
pH	6.5 to 8.5	Secondary guideline, not enforceable
TDS	500 mg/L	Secondary guideline, not enforceable
Iron	0.3 mg/L	Secondary guideline, not enforceable
Manganese	0.05 mg/L	Secondary guideline, not enforceable
Sulfate, chloride	250 mg/L each	Secondary guideline, not enforceable

Sources for the table: EPA primary standards, EPA secondary standards, the EPA PFAS rule page and the EPA radon rule record.

A few notes on reading these:

• PFAS rules are in flux. In May 2026 the EPA proposed keeping the PFOA and PFOS limits while letting public systems request two more years, to 2031, and separately proposed rescinding the 2024 limits for PFHxS, PFNA, HFPO-DA (GenX) and the mixture “hazard index.” Both are proposals, not final rules, as of October 2026.
• Secondary standards cover nuisance chemicals (taste, smell, stains) and the EPA doesn’t enforce them. pH still matters for your pipes: the EPA pairs corrosion and pH with lead testing.
• Lead and copper have “action levels” for public systems (lead at 0.015 mg/L, dropping to 0.010 mg/L on November 1, 2027), not MCLs.
• Your state may be stricter. Ask your health department which numbers to use.

If every result is under the standard, that’s genuinely good news. You don’t need a filter for safety reasons; keep testing once a year and when something changes.

What should you do if a result comes back high?

Don’t panic, and don’t start buying equipment yet. The EPA’s advice has two steps: contact your public health department for specific steps to follow, and retest to confirm the contaminant and its level. A single sample can be thrown off by sampling mistakes, especially for bacteria.

Meanwhile, the CDC suggests considering bottled water or another safe source, and your health department can help you understand the results. If you have health concerns, or someone in the house is pregnant, an infant or has a medical condition, talk to your doctor.

What usually comes next depends on what you found:

• Bacteria: the EPA lists runoff and septic effluent among the ways germs reach wells, and recommends a well cap or sanitary seal. Your health department may suggest an inspection and disinfection by a well or pump contractor, then a retest.
• Nitrate, arsenic, uranium, manganese or PFAS: these are in the groundwater itself, so the fix is usually treatment certified for that contaminant, or another water source. Our well water and water filter hubs explain the options, and reverse osmosis is one common route for drinking water (how reverse osmosis works).
• Radon: the EPA’s older guidance points to treating water as it enters the house, since most of the risk is from breathing it.
• Iron, sulfur smell, hardness: mostly nuisance problems with their own treatment options; see water softeners and whole-house filters.

Whatever you choose, test again afterwards. Treatment is only working if a lab says so.

The bottom line

A private well has no utility checking it, so the job is yours. The good news is that it’s a small job:

• Every year: total coliform bacteria, nitrate, TDS and pH, from a state-certified lab.
• At least once, then as advised: what your area calls for. Arsenic and radon are common natural ones; add pesticides, fuel compounds, metals or PFAS based on what’s nearby.
• Right away: after a flood or repair, when the water changes, or when a baby or pregnancy is in the picture.
• When something is high: retest, call your health department, and only then pick treatment certified for that contaminant.

Many wells pass every test, and those households don’t need a filter at all. Testing is how you find out which kind of well you have. For the next step, see Start here: test your water.