Well Water Testing 101

If your water comes from a private well, one fact drives everything else: private wells are not regulated under the Safe Drinking Water Act. No utility treats your water, and no agency routinely tests it. Testing — and paying for it — is entirely the well owner’s responsibility. The upside is that testing a well is straightforward once you know what to ask for.

Start with the two annual tests

The EPA recommends that private well owners test every year for the two indicators most likely to signal a problem, no matter where you live:

Total coliform bacteria (and E. coli). These indicate whether the well or wellhead is vulnerable to contamination from surface water, septic systems, or animals. Bacteria have no taste, smell, or color.
Nitrate. A concern near agriculture and septic systems. Nitrate is federally limited to 10 mg/L (as nitrogen) in public water, and it’s especially important if anyone in the household mixes infant formula, because high nitrate is dangerous for infants.

Add tests based on your area

Beyond the annual baseline, test for what’s plausible where you live:

Arsenic — naturally occurring in groundwater across many regions; no taste or odor.
Lead — mainly from your own plumbing rather than the aquifer, but worth a baseline.
Radionuclides such as uranium or radium in areas with certain granite or sedimentary geology.
PFAS if there’s a known industrial or firefighting-foam source nearby.

A local health department or state extension office can tell you which contaminants are common in your county.

How often, and when

Test the annual baseline once a year, and re-test any time you notice a change in taste, color, or odor, after any flooding, and after any work on the well or plumbing. Groundwater conditions change — a well that tested clean five years ago isn’t guaranteed clean today.

Use a certified lab

Do-it-yourself strips are fine for a rough check but aren’t a substitute for an accredited result. Use a laboratory certified for drinking-water analysis (many states publish a list of labs accredited under the National Environmental Laboratory Accreditation Program). Our state-by-state well-water guides point to where to find a certified lab in your state.

After you test

If a result comes back above a health-based guideline, test first and treat second — see our filter guides for which technologies are actually certified to remove the specific contaminant you found, so you’re not paying for treatment you don’t need.

Sources

US EPA — “Private Drinking Water Wells” — https://www.epa.gov/privatewells
US EPA — “Ground Water and Drinking Water” — https://www.epa.gov/ground-water-and-drinking-water
US EPA — “National Primary Drinking Water Regulations” — https://www.epa.gov/ground-water-and-drinking-water/national-primary-drinking-water-regulations