The short answer: the CDC and EPA recommend testing a private well at least once a year for total coliform bacteria and nitrate, since those are the two most common and most immediately health-relevant problems. On top of that annual check, run a broader panel (arsenic, lead, and anything else common in your area) roughly every three to five years, and test right away after specific events such as flooding, a repair, or a new baby in the home.
No one else tests your well, so this schedule is entirely on you. The good news: the yearly test is cheap and simple compared with the broader panels.
If your home is on a public water system, a utility tests it constantly and has to report the results. A private well has no such backstop. The EPA does not regulate private wells, so how often your water gets checked is a decision only the owner makes. Most owners test once when the well is drilled and then never again, which is exactly the gap this schedule is meant to close.
The annual test: bacteria and nitrate, every year
Both the US Centers for Disease Control and Prevention and the EPA recommend that private well owners test their water at least once a year for two things: total coliform bacteria and nitrate. These are the baseline checks for a reason.
- Total coliform bacteria is an indicator that surface water, and whatever it carries, may be reaching your well. A positive result is a signal to investigate your well's seal and, if E. coli is present, to stop drinking the water until it is fixed.
- Nitrate can rise seasonally with rainfall, fertilizer application, and septic activity, so a single old reading is not reliable. The EPA limit is 10 milligrams per liter (mg/L, measured as nitrate-nitrogen), a level set specifically to protect infants.
Because both of these can change from year to year, and both have real health consequences, the annual test is the one schedule item you should not skip. It is also the cheapest: a basic coliform-plus-nitrate test through a certified lab or your county health department is usually modest in cost.
The wider panel: every three to five years
Some contaminants change slowly, if at all, because they come from the geology your well draws through rather than from surface activity. Arsenic, for example, leaches from certain bedrock and tends to be stable over years. You do not need to test for these every year, but you should not test only once, either. The general guidance is a broader panel every three to five years, covering the contaminants that are plausible for your area.
What belongs on that wider panel depends on where your well is. Arsenic and radon are geological. Lead usually comes from older well components and household plumbing. Which of these is worth your money is a local question, which is what our guide on what to test your well water for works through.
Test right away after these events
Beyond the routine schedule, several events should trigger an immediate test regardless of when you last checked:
- Flooding or heavy runoff near the wellhead. Floodwater can carry bacteria and chemicals directly into a well. The CDC advises testing (and often disinfecting) any well that has been flooded before using the water.
- Any repair or replacement of the well, pump, or piping. Opening the system can introduce bacteria, so retest after the work is done.
- A change you can taste, see, or smell. New color, odor, oily film, or a metallic or salty taste all warrant a test, even though the most dangerous contaminants have none of these signs.
- A new baby, or a pregnancy, in the household. Because nitrate is specifically dangerous to infants under six months, test for it before an infant relies on the water. See our guide on nitrate and the risk to infants.
- A nearby land-use change. New agriculture, a fuel spill, industrial activity, or a neighbor's failing septic system can all affect your water.
- You just bought the home. A prior owner's test may be years old or may never have happened. Start your own record.
Regional risk is not a measurement of your own well
Knowing which contaminants are common in your area tells you what to test for and how urgently, but it cannot tell you what is in your specific well. Two wells on the same road can differ. Only a certified laboratory test measures your actual water. The schedule above is about making sure that test happens on time.
Where to get the test done
For an accurate result, use a laboratory certified by your state to test drinking water. Many county or state health departments run these tests directly or maintain a list of certified labs, and some offer free or low-cost annual coliform and nitrate testing to private well owners. The lab supplies a sample bottle and collection instructions; following the collection steps exactly matters, because a poorly collected bacteria sample can give a false positive.
Keep a simple record
Write down what you tested, when, and the result each year. A running record turns single numbers into a trend, so a nitrate reading creeping upward over three years is something you can catch and act on rather than a surprise. It also makes selling the home easier, since a buyer's inspector will ask.
Sources
- US Centers for Disease Control and Prevention. Private Well Water and Testing. Guidance recommending annual testing for coliform bacteria and nitrate, plus testing after flooding, repairs, or noticeable changes. cdc.gov.
- US Environmental Protection Agency. Private Drinking Water Wells. Recommended testing schedule and the note that the EPA does not regulate private wells. epa.gov/privatewells.
- US Environmental Protection Agency. National Primary Drinking Water Regulations. Maximum Contaminant Levels, including nitrate at 10 mg/L (as N). epa.gov.
Related guides
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