About 14.6% of US homes, roughly 20,490,900 households, get their water from a private well. EPA's drinking water limits apply to public water systems, not to private wells, so nobody tests your well unless you do. Most contaminants that matter have no taste, color or smell.
Every year: the four basics
EPA recommends testing a private well at least once a year for:
- Total coliform bacteria (and E. coli if coliform is found). The best single check that surface water or septic waste is reaching the well.
- Nitrate. From fertilizer, manure and septic systems. The limit for public water is 10 mg/L (as nitrogen), set to protect infants.
- pH. Acidic water (below 6.5) corrodes pipes and can pull lead and copper into the water.
- Total dissolved solids (TDS). A rough measure of everything dissolved in the water; a sudden change is a reason to look closer.
At least once, then as needed: depends on where you live
- Arsenic. Naturally present in rock across much of New England, the upper Midwest and the West. USGS estimates about 2,101,600 people use wells above the 10 microgram per liter limit. See our arsenic and nitrate guide.
- Uranium and radon. Common in granite regions. The uranium limit for public water is 30 micrograms per liter.
- Lead and copper. Usually from household plumbing rather than the aquifer, so take a first-draw sample from a tap you drink from.
- Iron, manganese and hardness. Mostly about staining, taste and scale, but manganese also has an EPA health advisory level of 0.3 mg/L.
- PFAS, pesticides or fuel compounds if you live near farms that spray, a military base, an airport, a landfill or a gas station.
Your state page shows modeled arsenic and nitrate for every county, which tells you what to prioritize.
Also test when
- You buy a home with a well (make a passing lab test a condition of the offer).
- The well floods, or the area around it does.
- You repair the well, replace the pump, or the taste, color or smell changes.
- Someone in the home is pregnant or you are mixing infant formula with well water.
Lab test or home kit?
Use a lab certified by your state for drinking water. Lab results are what lenders, buyers and health departments accept, and labs measure arsenic, uranium and lead at the levels that matter. Home test strips are fine for a quick look at hardness, pH or chlorine after shock treatment, but they cannot measure arsenic or uranium reliably and a negative bacteria strip is not proof.
Many states and counties run low-cost or free testing; your state page links the program and the certified lab list where we could confirm them. Mail-in kits from certified labs are the convenient option when there is no lab nearby.
How to take a good sample
- Follow the lab's bottle instructions exactly, especially for bacteria: sterile bottle, no touching the inside of the cap, and a deadline for getting it back to the lab.
- Sample cold water from a tap without a filter or softener in the line, unless you are testing whether your treatment works.
- For lead, take the first water out of the tap after it has sat for at least six hours.
- Keep every result. A history shows trends that one test cannot.
If a test comes back bad
Retest to confirm before buying equipment, then treat exactly what the lab found. Bacteria usually call for shock chlorination and a look at the well cap and casing; arsenic, nitrate and uranium call for reverse osmosis or a dedicated system. Our whole-house well filter guide walks through the order.