The checklist
What to Test Your Well Water For
Test your well water for the things that can hurt you and the things that wreck your plumbing. At the top of the list: bacteria, nitrate, hardness, iron, manganese, and sulfur. Add pH and total dissolved solids, and, depending on your area, radium, arsenic, lead, and PFAS. Here is the full checklist and why each one earns its place.
You do not need to run every test every year. Bacteria and nitrate belong on an annual schedule because they are invisible and can make you sick. The rest you test when you see a sign, when you are sizing treatment, or every few years as a baseline. Work down the list below and note which ones apply to your well.
- Coliform bacteria and E. coli. The single most important well test. These are indicator organisms: if they are present, surface water or waste is reaching your well and disease-causing microbes could be too. You cannot taste, see, or smell them.
- Nitrate and nitrite. Usually from fertilizer, septic systems, or animal waste. Above the EPA limit of 10 mg/L, nitrate is dangerous to infants and pregnant women. It is also a warning that surface contamination is reaching your aquifer.
- Hardness. Calcium and magnesium. Not a health risk, but Missouri wells commonly run 15 to 25+ grains per gallon, which scales water heaters and pipes, spots dishes, and wastes soap. This number tells you whether you need a softener and how big.
- Iron. Causes orange and red staining on sinks, tubs, and laundry plus a metallic taste. The secondary limit is 0.3 mg/L. Iron can also feed iron bacteria that clog plumbing and fixtures.
- Manganese. Leaves black or brown stains and gritty specks. The EPA has a health advisory for manganese that is stricter for infants, and the aesthetic limit is 0.05 mg/L.
- Sulfur and hydrogen sulfide. The rotten-egg smell, usually from sulfur bacteria or the local geology. Mostly aesthetic, but it corrodes metal, tarnishes silverware, and can point to bacterial activity in the well or heater.
- pH. How acidic or alkaline your water is. Low, acidic pH is corrosive and can leach copper and lead out of your plumbing; high pH worsens scale. The comfortable range is 6.5 to 8.5.
- Total dissolved solids (TDS). The overall mineral load. High TDS reads as salty, bitter, or flat water and helps explain your other results. The EPA secondary standard is 500 mg/L.
- Radium. A naturally radioactive element present in parts of Missouri's deeper aquifers. The EPA limit for combined radium-226 and radium-228 is 5 pCi/L. It is invisible and tasteless, so only a lab can find it.
- Arsenic. Occurs naturally in some Missouri groundwater. Long-term exposure is linked to cancer. The EPA limit is 10 parts per billion. Odorless and tasteless, so testing is the only way to know.
- Lead. Rarely in the aquifer itself; it usually leaches from older plumbing, solder, and brass fixtures, especially when water is acidic. The EPA action level is 15 parts per billion. Test the water as it comes out of your tap.
- PFAS. The so-called forever chemicals, which have been detected in St. Charles County-area water supplies, some above the EWG health guideline even while passing the federal test. In 2024 the EPA set enforceable limits for several PFAS. Detecting them takes a specialized lab.
If you only do one thing this year, collect a bacteria and nitrate sample through your county health department or the Missouri State Public Health Laboratory. Those two are the ones that can hurt someone and give no warning. Everything else on this list can wait for a sign or a comprehensive panel.
How to prioritize: test bacteria and nitrate every year. Test hardness, iron, manganese, and sulfur when you notice staining, scale, or odor, or when you are pricing treatment. Add a comprehensive panel with pH, TDS, radium, arsenic, and lead every few years or whenever you buy the home, drill or repair the well, or something in the water changes. If you are near known PFAS detections or industry, ask a certified lab about a dedicated PFAS test.