Private Well Water Testing: What to Test, How Often, and Why

Roughly 43 million people in the United States get their drinking water from private wells. Unlike municipal systems, private wells are not covered by the EPA’s Safe Drinking Water Act, which means no agency tests your water for you. The responsibility — and the cost — falls entirely on the homeowner, and surveys consistently find that most private wells are tested far less often than recommended.

The CDC recommends testing every well at least once a year for total coliform bacteria, nitrates, pH, and total dissolved solids. You should test more often, and for more contaminants, after specific triggers: flooding, a nearby land-use change (new septic, agriculture, or industry), a noticeable change in taste, color, or odor, or the replacement of any part of the well system. A real-estate transaction almost always requires a fresh certified test.

Beyond the annual basics, screen periodically for region-specific risks. Arsenic and uranium occur naturally in many bedrock aquifers; nitrates spike near agricultural and septic activity and are especially dangerous for infants; lead can leach from older plumbing; and radon, VOCs, and pesticides appear in particular geologies and land uses. Your state health department or local extension office can tell you which contaminants are common in your area.

Counter-intuitively, bacterial contamination of wells tends to peak in summer. Warm water (90°F and above) and heavy summer rainfall that flushes surface contaminants into shallow aquifers both raise the odds of a positive coliform result — so a mid-summer test is a good annual habit.

Always use an EPA-certified or state-certified laboratory, or one accredited under NELAP. Only results from a certified lab are accepted for real-estate closings, mortgage requirements, and regulatory follow-up — and certified labs follow validated chain-of-custody and analytical methods, so the numbers actually mean what they say.