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.