How often to test well water

Best for

Every private well owner who wants a simple calendar for routine and event-driven testing.

Wrong fit

Anyone with a current health-based problem such as E. coli or high nitrate. Follow your health department's retest schedule instead of this routine one.

Tradeoff

Agencies differ slightly on timing. Following the most cautious advice costs a little more, but catches changes sooner.

The baseline: what every well needs

CDC says to test your well water at least once every year for total coliform bacteria, nitrate, total dissolved solids (TDS) and pH. EPA gives the same yearly list. That’s the floor for every private well.

Other agencies stretch some of those intervals and add tests:

The simplest safe plan is to follow the most frequent schedule: coliform, nitrate, pH and TDS every year, plus arsenic and lead at least once.

A year-by-year schedule

Your state health department knows which contaminants are common where you live. Browse state guidance at /states/.

Test right away after these events

CDC says to test more often, or for more contaminants, when:

• You’re told 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 your well system.
• You notice a change in taste, color or smell.
• Someone in the home becomes pregnant.
• A child starts living with you.

EPA adds known groundwater problems and nearby construction to the list, and says to test more often when young children, older adults, or pregnant or nursing people live in the home.

After a positive bacteria test

A positive result starts its own schedule. After you shock chlorinate:

If coliforms return, CDC says to repeat the disinfection and contact your health department if they persist. See shock chlorination and bacteria in well water.

After installing treatment

Equipment can fail quietly. Testing is how you know it’s still working.

• Any system. Test the treated water after installation. Both Connecticut’s Department of Public Health (DPH) and Minnesota’s health department say so.
• UV disinfection. Connecticut DPH recommends monthly coliform tests for at least the first six months, then testing raw and treated water every year.
• Reverse osmosis. Connecticut DPH says to test raw and treated water annually, or quarterly to semi-annually when contaminant levels in the raw water are high.
• Iron filters, softeners and neutralizers. Retest the treated water for the target problem at least yearly. A slow decline is easy to miss.

When you test, label each sample: raw (from the pressure tank spigot) or treated (from a tap after the equipment). Penn State points out that a faucet sample in a home with treatment reflects the treated water, not the well.

Timing tips

• Bacteria vary with weather. Penn State says wells tend to show the most bacteria after several weeks of wet weather and the least in cold, dry winter conditions. A test after a wet stretch is the tougher test.
• Wait after shocking. CDC says to wait 7 to 10 days, and until chlorine is flushed, before sampling for bacteria.
• Keep records. Penn State notes past test results can matter if you ever need to show that a nearby land use changed your water. Keep every report in one folder, with the date and where the sample was taken.

A sample testing calendar

One way to keep it simple is to tie testing to a date you already remember, such as a birthday or the start of spring. For a typical household:

If you have treatment equipment, add a treated-water sample to the yearly test so you can see whether it’s still working.

Check the well, not just the water

Testing tells you what’s in the water. A yearly look at the well helps keep it that way. EPA suggests checking exposed parts of the well for cracks, corrosion, a missing cap or settling around surface seals, keeping a well cap or sanitary seal in place, and pumping and inspecting your septic system as your local health department recommends. A damaged cap or a casing cut off below ground is a reason to test for bacteria sooner.

Keep a well file

Penn State notes past test results can matter if you ever need to show that nearby land use changed your water, and that samples documenting water quality before a land disturbance should be collected by an unbiased professional. Keep:

• Every lab report, with the date and where the sample was taken.
• Notes on shock chlorination, repairs and pump work.
• Treatment equipment installs, settings and maintenance dates.

While you wait for a retest

A retest takes days to weeks. In the meantime:

• After a positive coliform or any E. coli result, use bottled or boiled water for drinking and cooking until a retest is clean. Penn State says boiling water for about one minute kills bacteria.
• Take E. coli seriously. Penn State says a positive E. coli result is more serious than coliform alone because it indicates human or animal waste is entering the water.
• Look for the cause. Check the well cap, casing and grading, and the septic system if E. coli was found.
• Don’t buy equipment yet. A single positive result calls for shock chlorination and a retest first. See shock chlorination.

What this costs

The yearly basics are the cheapest part of owning a well. Penn State describes total coliform testing as inexpensive, generally $10 to $30. Broader panels cost more, so many owners run a full panel once, then just the core tests each year. For lab options, see well water test kits compared. For step-by-step sampling, see how to test well water.