As of 2026-10-07. Federal guidance and limits are from US EPA. EPA says private wells aren't regulated under the Safe Drinking Water Act nor by most states, and state rules and required tests vary, so check with your state and local health department.
Why wells need extra attention
EPA says private well owners "are responsible for delivering safe drinking water to their households." EPA also cites a US Geological Survey study of 2,100 private wells in which about one in five contained at least one contaminant above a human-health benchmark.
The short version
Find your state's private-well program (EPA keeps a directory) and ask the local health department whether any tests or inspections are required at sale where you're buying. Ask your lender, too.
Test the water at a state-certified lab. EPA's baseline for wells is total coliform bacteria, nitrate, total dissolved solids, and pH, plus other tests based on local conditions.
Ask the seller for records: well type and depth, construction record, past test reports, treatment equipment, pump age, repairs, flooding history, septic location.
Point things out to your inspector or a licensed well contractor: drainage around the well, the cap or sanitary seal, the casing, nearby chemicals, fuel tanks, septic system, and any old wells.
If a result is high: EPA says to contact your public health department for specific steps and re-test to confirm.
Talk to your attorney or agent about how testing fits your contract. That's outside the scope of this page.