Iron in water is common in parts of the St. Louis area and in many private wells, and it often shows up as stains rather than as a clear warning. Brown or orange marks on sinks, tubs, toilet bowls, and laundry are the most common sign. Iron can also give water a metallic taste. These signs are useful, but they are not proof on their own, so the next step is to observe carefully and then test.
Notice where the stain appears
Look at where the staining happens. Iron stains usually appear on fixtures and in laundry wherever water sits, and they can be reddish-brown or orange. Check whether the stain appears on both hot and cold taps or only on hot. Staining only on the hot side can point to the water heater or hot water lines instead of the supply, which is a plumbing question rather than a treatment question.
Watch the water as it sits
Fill a clear glass from the cold tap and let it stand for a while. Water that starts clear and then turns cloudy or brown as it sits can contain dissolved iron that oxidizes when exposed to air. Compare this with a glass filled from a tap you have not run for a long time, since stale water in the pipes can look different. This observation does not identify iron on its own, but it adds to the picture.
Separate iron from copper and from old pipes
Blue-green stains come from a different source than brown or orange ones, and rust-colored water can come from aging galvanized pipes inside the home. If you have older pipes, the staining may come from the plumbing itself. Ask a plumber to check the pipes if you are unsure, and keep that check separate from the water test.
Test before you buy
The only reliable way to know whether iron is present, and how much, is a test of your water by a certified laboratory. Home test kits can give a rough reading, but a lab gives you numbers you can compare across companies. Ask the lab to test for iron and manganese, since both can cause staining, and ask for the report to list both values. Bring the report to any treatment company you consider.
Ask the company what the test shows
When a company reviews your report, ask them to explain what the numbers mean for the equipment they propose, and whether the equipment is designed for the type of iron in your water. Dissolved iron, particulate iron, and iron bound to other materials are handled differently. A company that cannot explain the difference should not be selling you a solution yet.
Start with the observation, then the test
You do not need to buy equipment because your sink is stained. Watch where the stains appear, note how the water behaves in a glass, and get a lab test. Those three steps give you the facts you need to decide what to ask for next.