How Often Should You Test Your Well Water?

The yearly minimum is a test for total coliform bacteria and nitrate, plus anything of known concern in your area. These two top the schedule because they change with the seasons and the land around your well, they can make someone sick, and they give no warning in taste, color, or smell.

Spring is a sensible time to sample, after the wet season and before heavy summer use, so you catch anything the runoff brought in. The low-cost route is a kit from your county health department or the Missouri State Public Health Laboratory: pick up a sterile bottle, follow the collection steps exactly, and return it within the hold time.

What counts as a local concern is worth a quick call to your county health department before you sample. In some areas that means adding arsenic or radium to the panel; near heavy row-crop agriculture it often means watching nitrate more closely. A one-minute question tells you whether the standard bacteria-and-nitrate kit is enough or whether to add a line or two.

Every three years or so, run a fuller chemistry panel: hardness, iron, manganese, sulfur, pH, and total dissolved solids, plus radium, arsenic, and lead in areas where they occur. Wells drift slowly as they age and as the aquifer shifts, so a periodic baseline catches trends before they turn into stained fixtures, scaled heaters, or a health problem.

This panel does double duty: it tells you whether any treatment you already own, a softener or a filter, is still keeping up. Equipment wears out and media exhausts, and the only way to confirm it is still working is to test the water coming out of it. A number that has crept year over year is your early warning; a number that jumped is your signal to act now.

Some events call for an immediate test, regardless of when you last sampled. Test right away when any of these happen:

• A baby is on the way or an infant will drink or mix formula with the water. Nitrate is a specific danger to infants, so confirm it before they arrive.
• The taste, smell, or color changes even a little. A new metallic taste, rotten-egg odor, or cloudiness means something in the water changed and is worth a test.
• Your well floods or is submerged or nearby wells do. Floodwater is the most common way bacteria get into a well.
• New industry, drilling, a spill, or heavy agriculture starts nearby. Land-use changes upgradient of your well can reach the aquifer.
• You repair, replace, or open the well, pump, or pressure tank. Any time the system is opened, disinfect and retest before drinking.
• A test is required for a home sale or loan. Lenders often require a recent bacteria and nitrate result at closing.
• Someone has recurring stomach illness with no clear cause. Rule the water in or out with a bacteria test.

Keep your results in one folder, dated. A short history of tests turns a single confusing number into a trend you can act on, and it is exactly what a treatment company or lab will want to see when you ask what to do next.