Why private wells are different

Municipal water systems are regulated under the Safe Drinking Water Act (SDWA) and must test for dozens of contaminants, report results annually in Consumer Confidence Reports, and take action when limits are exceeded. None of this applies to private wells. The EPA, your state, and your county do not monitor your well water. You are your own water utility.

This is not cause for alarm — the majority of private wells in the U.S. produce safe drinking water. But elevated contaminants can exist without any taste, odor, or visible sign. The only way to know is to test.

What to test for — and when

The EPA recommends testing private wells at least once a year for bacteria and nitrate, and whenever you notice a change in water quality, taste, or odor. Additional contaminants to test for depend on your geography, well depth, and local land use.

Annual testing (minimum)

One-time baseline testing (if never done)

If you have never had a comprehensive test, the following should be on your first panel:

Test whenever:

Understanding your results

Lab reports list contaminants with your measured concentration and a comparison to the relevant standard. Key terms to know:

Term What it means
MCL (Maximum Contaminant Level) The enforceable legal limit for public water systems. Private wells are not legally required to meet MCLs, but they are the best available health benchmarks.
MCLG (Maximum Contaminant Level Goal) The level at which EPA believes there is no health risk. For carcinogens (arsenic, lead, PFAS), MCLG is often 0 — meaning any level carries some risk. The MCL may be set higher than the MCLG due to treatment feasibility.
Health Advisory A non-enforceable guidance level, often set for populations at specific risk (e.g., fluoride Health Advisory for children).
ND or <MDL Not detected / below the method detection limit. Does not mean the contaminant is absent at all concentrations — it means the lab could not detect it at its measurement threshold.
µg/L or ppb Micrograms per liter = parts per billion. The units used for most heavy metals and organic contaminants.
mg/L or ppm Milligrams per liter = parts per million. Used for nitrate, fluoride, hardness, and other parameters measured at higher concentrations.
pCi/L Picocuries per liter. The unit for radioactive contaminants (radium, radon). A radioactivity unit, not a mass concentration.

Geography matters: what to test based on where you live

Groundwater contaminants follow geology, not political boundaries. Your aquifer type and local geology are the strongest predictors of what might be in your well water. Use our state and county resources to understand local patterns:

Explore Michigan well water data by county

When you find a problem

A result above an MCL (or above the MCLG for carcinogens) does not require panic — but it does require action. The right response depends on what was found:

Find a certified lab and learn proper sampling technique

Contaminant guides

Detailed information on each contaminant covered in private well water testing: