Many homes in O'Fallon and the surrounding parts of St. Charles County rely on private wells, and the depth of a well shapes what you are most likely to find in the water. A shallow well and a deep bedrock well can look the same at the faucet, yet they draw from different sources and carry different concerns. Before you decide on testing, filtering, or changes to your softener setup, it helps to know which type you have. Here is how to tell at home.
Why depth matters
Shallow wells draw from groundwater near the surface. That water can pick up material that moves down from the land above, including runoff from fields, leaks from septic systems, and surface water that gets in through a cracked casing or a loose cap. Deep wells draw from bedrock aquifers farther down. Those sources are usually better shielded from surface activity, but they can carry naturally occurring minerals. Homeowners with deep wells in the area often think about naturally occurring radium, gross alpha, and uranium. Homeowners with shallow wells near row-crop farming or septic systems often watch for nitrates and coliform bacteria. Neither type is automatically better for every test, so each one needs its own plan.
Start with the paperwork
If you have a well log or completion record, read it first. These records usually list the depth of the well, details about the casing, and the year it was drilled. If you do not have one, ask the previous owner, check your closing file, or contact the state agency that keeps water well records. Also ask whether earlier water tests were done and where the results are kept. Old results will not replace new testing, but they give you a starting point.
Walk the wellhead
- Is the well cap intact and snug, with no cracks, gaps, or missing screens where insects or surface water could enter?
- Does the casing stand clear of the ground, with soil sloping away from it?
- Is the well a safe distance from septic tanks, drain fields, fertilizer storage, and livestock areas? A property map or survey can help you check.
- After heavy rain, does water pool around the wellhead?
Notice what the water shows you
Changes in the water can hint at what is happening underground. Cloudy or rusty water, orange or black staining, and a rotten-egg smell can point to iron, manganese, or sulfur bacteria. Black slime in toilet tanks or on fixtures is a common sign of iron bacteria. Water that shifts after a heavy storm or a spring thaw may suggest shallow-well influence. These signs do not tell you what is in the water. They tell you where to test.
Match your testing to your well type
For a shallow well, start with coliform and E. coli testing, then consider nitrates, especially if the well sits near farmland or a septic system. If slime or staining is present, ask about iron bacteria testing. For a deep well, ask a lab about radium, gross alpha, and uranium, along with general measures such as hardness and iron. The Missouri State Public Health Lab offers coliform, E. coli, and iron bacteria testing. For other constituents, a certified outside lab is the usual route, so compare what each lab tests for before you send a sample.
Plan your next steps
- Confirm your well type from the records and the wellhead.
- Write down what you see, smell, and notice in the water, with dates.
- Choose tests that match your well type and your observations.
- Ask the lab for sampling instructions, since each test may need its own container and handling.
- Review the results before you change equipment. A softener handles hardness, but it does not address every concern a well can carry.
If results show a concern, a county health office or a licensed well professional can help you understand the next steps for your property. Keep your well records and test results together so you can share them easily when needed. Good records make future decisions about your water in O'Fallon much simpler.