How often should you test your well water, and what should you test for?

The yearly baseline: four tests

The EPA's guidance for private well owners is short: test your private well annually for total coliform bacteria, nitrates, total dissolved solids and pH. The CDC gives the same list, phrased as at least once every year, and adds a fifth line that matters as much as the first four: other germs and chemicals of concern in your area.

Nobody else is going to run those tests for you. The EPA estimates that more than 23 million US households rely on private wells, and it notes that water from private domestic wells is not regulated by the federal government under the Safe Drinking Water Act, nor by most state governments. Its private well page puts it plainly: private well owners are responsible for delivering safe drinking water to their households.

The reason to keep at it every year, rather than testing once and moving on, is that well water does not stay the same. The Minnesota Department of Health recommends a coliform test every year even if nothing about the water seems different, because water quality can change. Washington State's Department of Health notes that nitrate in wells can vary throughout the year. And the EPA's private well page cites a U.S. Geological Survey study of 2,100 private wells in which about one in five contained at least one contaminant above a human-health benchmark for drinking water.

When to test sooner than a year

The EPA lists four situations that call for a test right away rather than at the next annual date: known problems with groundwater or drinking water in your area; significant changes near the well, such as flooding, land disturbance, new construction or industrial activity; replacing or repairing any part of the well system; and a change in the water's odor, color or taste. The CDC's list is nearly identical and adds two household changes: you or someone you live with becoming pregnant, or a child starting to live with you.

The EPA also suggests testing more often if small children or elderly adults live in the house or someone is pregnant or nursing. State agencies add their own triggers. The Minnesota Department of Health tells owners to test for coliform bacteria any time the well or water system is worked on, and to test the well before bringing a new baby home. Washington State's Department of Health says that if a nitrate result is 5 mg/L or higher, you may want to re-sample in six months.

What to add for your area

The four routine tests are a floor, and your surroundings decide what goes on top. The EPA publishes a table that matches nearby activities and household signs to tests, and it works like a checklist. Near intensive agriculture: nitrate, nitrite, pesticides and coliform bacteria. Near gas drilling: chloride, sodium, barium and strontium. Near coal or other mining: metals, pH and corrosion. Next to a dump, junkyard, landfill, factory, gas station or dry cleaner: volatile organic compounds, total dissolved solids, pH, sulfate, chloride and metals.

The same table covers what you notice inside the house. Plumbing or service lines that contain lead point to pH, lead and copper. Stained fixtures or laundry point to iron, copper and manganese. Scaly residue and soap that will not lather point to hardness. A salty taste, or a heavily salted road nearby, points to chloride, total dissolved solids and sodium. Where radon shows up in indoor air or the region is radon rich, the EPA lists radon.

Some states recommend one-time tests for everyone. The Minnesota Department of Health asks well owners to test for arsenic at least once and for lead at least once, alongside coliform bacteria every year. The CDC's advice is the general version of the same idea: contact your health department to find out what other germs or chemicals to test for based on where you live.

Where to send the sample

Use a certified lab. The EPA says to use only laboratories certified to do drinking water testing, and points owners to a state certified laboratory or to the local health department, which may provide private well testing for free. The CDC says the same in fewer words: use a state-certified laboratory. On its page about secondary standards, the EPA adds that a list of certified labs is available from your state's laboratory certification officer.

The lab usually supplies the container. The Minnesota Department of Health suggests contacting an accredited laboratory for sample containers and instructions, or asking your county environmental or public health services whether they test well water. Follow the lab's own collection instructions. Prices vary by state and by test; Washington's Department of Health, for example, says many certified labs there charge $25 to $50 per test.

If a result comes back high

The EPA's advice is to contact your public health department for specific steps to follow and to have the well re-tested to confirm the contaminant's presence and concentration. The CDC also points to the local health or environmental department, which can help you understand the results and what to do next, and says that if results show harmful germs or chemicals, you should consider drinking bottled water or water from another safe source.

For coliform bacteria specifically, the Minnesota Department of Health lays out a sequence: use boiled or bottled water or a safe alternative source, disinfect the well with a chlorine solution, and test again after disinfection to confirm there are no coliform bacteria. It also cautions that if nitrate or arsenic were detected too, boiling may not be the safest option, because boiling water that contains those contaminants can increase their concentration.

This guide summarizes public guidance from the EPA, the CDC and state health departments. It is not medical advice and does not tell you whether your water is safe to drink. For what a specific result means for your household, ask your certified lab or your local or state health department.

Common well testing mistakes

Treating one clean report as the answer. A single test is a snapshot. The EPA and the CDC both describe testing as a yearly job, and Minnesota's health department recommends a coliform test every year because water quality can change.

Testing only for bacteria. Coliform is the test most people have heard of, but the yearly list also includes nitrate, total dissolved solids and pH, and both federal agencies tell owners to add local risks on top. Skipping the retest after work on the well is the other common gap: the EPA lists replacing or repairing any part of the well system as a reason to test immediately.

Losing the paper. A report you cannot find next year cannot show you a trend. The EPA tells well owners to keep accurate records of well maintenance, and keeping each year's lab report with those records is what lets you see whether nitrate is creeping up or holding steady. WellLedger, for example, keeps the next test date in view with reminders 30 days and 7 days ahead and on the day, and keeps each year's numbers next to a photo of the report.

Frequently asked questions