Well water testing: what to test, when, and how

Water that looks, smells, and tastes fine can still carry bacteria, nitrate, or arsenic. Testing is the only way to know. Private wells aren't covered by the federal rules that require public water systems to test, so it's up to the owner.

The yearly basics

EPA recommends testing private wells every year for:

• total coliform bacteria, a sign that surface water or waste may be getting in;
• nitrates, from fertilizer, septic systems, and animal waste, which are especially risky for infants;
• total dissolved solids (TDS), a general measure of dissolved minerals and salts;
• pH, which shows whether water is corrosive enough to dissolve metals from plumbing.

These tests are usually inexpensive, and many county health departments offer them or can refer you to a lab.

When to test more

Test again, and more widely, when:

• you buy a home or move into one with a well;
• the water's taste, smell, or color changes;
• there's been flooding near the well (see after a flood);
• the well, pump, or plumbing has been worked on;
• someone in the home is pregnant, or there's an infant;
• a neighbor finds a problem, or there's a known contamination source nearby, such as a fuel spill, a landfill, heavy agriculture, or mining.

Tests that depend on where you live

EPA's contaminant guide covers naturally occurring substances that vary with the local geology. They include arsenic, uranium, radon, fluoride, manganese, and iron. Your county or state health department usually knows which are common in your area. Lead and copper mostly come from plumbing rather than the aquifer, so test for them if the home has older plumbing or the water is corrosive.

Choosing a lab

Use a lab certified by your state for drinking water testing. Your state drinking water or health agency keeps the list. Home test strips are fine for curiosity but not for health decisions. Ask the lab for sample bottles and instructions before you collect.

Taking a good sample

• Follow the lab's instructions exactly. Bacteria samples usually have to reach the lab within a set number of hours, kept cool.
• For bacteria, remove any aerator and sample from a cold tap that doesn't have a treatment device on it, unless you're testing the treated water.
• Don't touch the inside of the bottle or cap.
• Note whether the sample is before or after any softener or filter.

Reading the report

The lab will give each result in mg/L or µg/L, often with a reference limit. Our well water test reader puts your numbers next to EPA's health-based and secondary standards and explains each one.

If bacteria show up

A positive coliform result often means retesting and inspecting the well cap and casing. If it's confirmed, the usual next step is disinfecting the well. Penn State Extension recommends retesting for coliform about 10 to 14 days after shock chlorination, then again two to three months later. See shock chlorinating a well. If E. coli is present, stop drinking the water unboiled and call your health department.

Radon in well water

Standard well tests don't include radon. If you live in a higher-radon area, see radon in well water on our sister site Radon by ZIP.

Testing triggers at a glance

Beyond the yearly basics, CDC and EPA recommend testing when:

• you hear about problems with well water in your area;
• there's flooding, land disturbance or a nearby waste disposal site;
• you replace or repair any part of the well system;
• the water's taste, color or smell changes;
• someone in the home becomes pregnant, or a child comes to live with you.

EPA also suggests testing more often if small children or older adults live in the home, or if someone is pregnant or nursing.

Matching tests to your surroundings

EPA's well-testing chart pairs nearby conditions with tests:

Condition nearby	Test for
Recurring stomach illness	Coliform bacteria
Lead plumbing or service lines	pH, lead, copper
Radon-rich region	Radon
Intensive agriculture	Nitrate, nitrite, pesticides, coliform
Coal or other mining	Metals, pH, corrosion
Gas drilling	Chloride, sodium, barium, strontium
Landfill, junkyard, gas station or dry cleaner	VOCs, TDS, pH, sulfate, chloride, metals
Fuel odor or buried fuel tanks	VOCs
Salty taste or road salt nearby	Chloride, TDS, sodium

CDC adds that you can ask your health department, your environmental department, or EPA's Safe Drinking Water Hotline at (800) 426-4791 which contaminants are a concern where you live.

Understanding indicator tests

CDC explains that coliforms, pH and total dissolved solids are "water quality indicators." They usually aren't harmful themselves, but they tell you something else may be wrong. Total coliform bacteria travel by the same routes as disease-causing germs and are much easier to test for. A positive E. coli or fecal coliform result likely means fecal contamination. A pH that's too low or too high can damage pipes and release metals like lead.

What to do with the results

• Compare each result with EPA's drinking water standards. Your lab report may already do this.
• If something exceeds a health standard, CDC suggests switching to bottled water or another safe source and contacting your local health department.
• Retest to confirm before investing in treatment.
• Keep every report to track trends over time.

Key takeaways

• Test every year for coliform, nitrate, TDS and pH.
• Add tests based on local conditions and EPA's chart.
• Use a state-certified lab.
• Act on any health-standard exceedance, and retest after treatment.

Frequently asked questions

Are home test kits good enough? They can help with screening, but CDC recommends state-certified laboratories for reliable results, especially for bacteria and nitrate.

How much does testing cost? It varies by lab and test package. Ask your local health department, since some test for free or at low cost.