Well Water Testing: Frequently Asked Questions

In Missouri, testing a private well is the owner's responsibility, because no agency does it for you. The simplest route is a bacteria and nitrate kit from your county health department or the Missouri State Public Health Laboratory: you pick up a sterile bottle, follow the collection steps exactly, and return it within the required hold time. For a fuller picture of hardness, iron, sulfur, and metals, use a certified drinking-water lab or have a qualified water-treatment company run an in-home test. Use a certified lab for anything health-related.

Test at least once a year for bacteria and nitrate, which change with the seasons and give no warning in taste or smell. Run a comprehensive panel for hardness, iron, manganese, sulfur, pH, and metals every three years or so. Beyond that schedule, test right away whenever something changes: a new baby in the home, a new taste, odor, or color, flooding near the well, new industry or agriculture nearby, or any repair to the well, pump, or pressure tank.

Start with bacteria, meaning coliform and E. coli, and nitrate, the two that can make someone sick without any warning. Add hardness, iron, manganese, and sulfur, which cause most of the staining, scale, and odor complaints in Missouri. Round it out with pH and total dissolved solids, and, depending on your area, radium, arsenic, lead, and PFAS. Test the invisible health contaminants on a schedule, and test the aesthetic ones when you see a sign or when you are sizing treatment.

The rotten-egg smell is hydrogen sulfide gas. It comes either from the local geology and decaying organic matter, or from sulfur bacteria that grow in the low-oxygen environment of a well or water heater. If the smell is only on the hot side, the water heater's anode rod is usually the source. It is mostly an aesthetic problem, but it corrodes metal, and it can be removed without chemicals using aeration and oxidizing filtration.

Orange, red, and brown staining is iron, which Missouri groundwater dissolves out of iron-rich rock and soil. If your water is clear at the tap and rusts as it sits, it is dissolved clear-water iron; if it is already orange from the tap, it has oxidized in the well. Black or brown staining usually means manganese is traveling with it. A softener removes only small amounts of iron; heavier iron needs an oxidizing iron filter, sized to a test.

Not necessarily. Clear water only tells you about the aesthetic layer, not the safety layer. Bacteria, nitrate, arsenic, radium, and lead are invisible, giving no color, odor, or taste at the levels that matter, so a well can look perfect and still fail a bacteria test. The only way to know clear water is safe is a lab test for bacteria and nitrate, repeated every year.

Hard, and often very hard. Most of the region runs about 8 to 19 grains per gallon, and private wells commonly run 15 to 25 grains per gallon or more, well above the USGS very-hard threshold of 10.5 grains per gallon. By comparison, treated municipal supplies in the area run lower, roughly 7 to 10 grains per gallon. Hardness is not a health risk, but at these levels it scales water heaters and pipes, spots dishes, and wastes soap, which is why many well owners here run a softener.

You need one if your water tests positive for coliform bacteria, and it is a sensible safeguard on many wells because bacteria can come and go with the seasons. A UV disinfection lamp inactivates bacteria and viruses as water passes it, with no chemical taste, and it is the standard fix after a well tests positive and has been disinfected. If your bacteria tests are consistently clean you may not need one, which is another reason to test first.

In the St. Charles County area you have two main options. For bacteria and nitrate, contact your county health department or the Missouri State Public Health Laboratory, which provide sample bottles and low-cost analysis. For a fuller panel, or to size treatment for hardness, iron, or sulfur, use a certified drinking-water lab or a reputable local water-treatment company. Some local companies, including our recommended provider, offer a free in-home water test an owner runs at your sink.