Private well water testing: the complete checklist

More than 40 million Americans and millions of Canadians drink from private wells. Unlike city water, private wells are not regulated under the U.S. Safe Drinking Water Act — nobody tests them unless the owner does. If you’re on a well, you’re the utility.

The annual baseline

The CDC recommends testing private wells at least once a year. At minimum, test for:

• Total coliform bacteria and E. coli — a sign that surface water or sewage is getting in.
• Nitrate — from fertiliser, manure and septic systems. Critical if an infant drinks the water.
• pH and total dissolved solids (TDS) — indicators of corrosiveness and general water quality.

Test in spring or early summer when runoff is highest, and use a state-certified drinking water laboratory — your local health department can point you to one, and some offer free or subsidised kits.

Every 3–5 years (or once, then as needed)

Depending on your geology and land use:

• Arsenic — common in parts of New England, the Upper Midwest, the Southwest and the Pacific Northwest.
• Uranium and radium — granite and some sandstone regions.
• Lead and copper — especially with older plumbing or acidic (low-pH) water.
• Hardness, iron and manganese — the usual cause of stains and metallic taste.
• Fluoride — naturally high in some aquifers.
• PFAS — if you’re near an airport, military base, fire-training area, landfill, or a farm that received biosolids.
• Pesticides or VOCs — near intensive agriculture, gas stations or industry.

Test immediately if…

• The well flooded or was submerged.
• You notice a change in taste, odour, colour or cloudiness.
• Someone in the home has unexplained stomach illness.
• The well was repaired, the pump replaced, or the cap damaged.
• A new baby is coming home, or someone is pregnant.
• There’s a known spill or new land use nearby.

Collecting a good sample

Use the bottles the lab provides and follow their instructions exactly. For bacteria: remove the aerator, disinfect the faucet tip, run cold water for several minutes, don’t touch the inside of the bottle, keep it cold and get it to the lab within the holding time (often 24–30 hours).

Reading the results

Compare to the same limits used for public water — see the contaminant library:

Result	What to do
E. coli present	Stop drinking untreated water. Boil or use bottled water, shock-chlorinate the well, inspect the cap and casing, retest. Consider NSF/ANSI 55 UV.
Total coliform present (no E. coli)	Shock-chlorinate and retest; find the entry point.
Nitrate above 10 mg/L (as N)	Don’t use for infant formula. Don’t boil — it concentrates nitrate. RO or ion exchange.
Arsenic above 10 ppb	RO certified for the arsenic form present, or specialised media.
Hardness, iron, manganese	Softener or oxidising filter sized from your results.

Protecting the well itself

• Keep the well cap intact and above ground, sloped so water drains away.
• Keep fertilisers, pesticides, fuel and pet waste away from the wellhead.
• Pump your septic tank on schedule (typically every 3–5 years).
• Seal and properly abandon unused wells on the property.

Bottom line

Test every year for bacteria and nitrate, test once for the regional suspects, and test again whenever something changes. Not sure where to start? Get a free well water plan.