An orange or rust-colored stain in a bathroom sink is one of the most common things St. Louis homeowners notice and then wonder about. Iron in the water is a frequent cause, but it is not the only one. Sink stains can come from the faucet, the drain, the plumbing above the sink, or something left sitting in the basin. The location and shape of the stain usually tell you where to start.

Start with where the stain sits

Look closely before you scrub anything. Stain placement is the most useful clue you have.

  • Around the faucet base or under the handle: Water may be leaking through the faucet body, or minerals may be collecting where water splashes and dries.
  • On the aerator screen at the tip of the faucet: Particles in the water can collect in the screen and leave a rust tint on the surrounding metal.
  • At the drain opening or inside the overflow slot: Water that sits in the basin, or residue from the drain assembly, often causes this pattern.
  • Across the whole basin floor: A spread-out stain that appears after running water points more toward the supply water itself.

Run the water and watch

Run the cold tap for a few minutes, then fill a clear glass and hold it up to a window or light. Water that looks clear when drawn and turns orange or tinted after sitting is a sign that dissolved iron is oxidizing once it meets air. That is a classic pattern in St. Louis tap water, and it is different from water that looks rusty the moment it comes out.

Next, compare hot and cold. If only the hot side leaves stains, the water heater or its anode rod may be contributing, and the hot water pipe should be part of your check. If both sides stain the same way, the source is more likely the supply or the fixture itself.

Check the faucet and drain

Remove the aerator and rinse it under running water. Look at the screen for orange grit or flakes. If the screen is clogged with debris, the stain may be coming from particles caught there rather than from the water flowing through clean. Next, inspect the drain stopper and the overflow opening with a flashlight. Rust-colored residue that rubs off easily on a white cloth can come from metal parts wearing down, while a hard, crusty film is more often mineral scale.

Look for other iron signs in the house

Iron staining rarely shows up in just one place. Check other fixtures for the same pattern. Look at the toilet bowl, the bathtub, laundry, and any white fabrics that have been washed in the same water. If several fixtures show the same orange tint, the source is probably the water supply. If only the bathroom sink shows it, the cause is more likely local to that sink.

Test the water before you assume

A visual check can narrow things down, but it cannot confirm iron. A simple home test kit can show whether iron is present, and a certified laboratory test will give you a clearer picture of the amounts involved and whether other minerals are part of the problem. If you are on a well, testing is especially worth doing. If you are on city water in St. Louis, ask for the most recent water quality information from your water provider, since it may already describe typical conditions in your area. Keep in mind that a water report describes the water at the treatment plant or at sampling points, not necessarily what your own pipes deliver after years of use.

Clean the stain carefully

Once you know the cause, cleaning helps. For iron stains, a cleaner made for rust removal on porcelain or stainless steel is usually the right tool, applied according to the label. Test a small hidden spot first, since some cleaners can dull finishes. Avoid mixing cleaning products, and rinse thoroughly after use. Cleaning removes the stain but does not fix a leak or the source of iron, so the stain may return if the cause is still present.

When to call a professional

Consider calling a licensed plumber if the stain grows, if you see water pooling under the sink, if the faucet drips, or if the stain comes back quickly after cleaning. A plumber can check the supply lines and shutoff valves. If testing shows meaningful iron in your water, the next step is a conversation about water treatment options, and that is a decision best made after you understand the test results and your household's needs.

The short version

Start by reading the stain's location. Run the water and compare hot and cold. Inspect the aerator and drain. Check other fixtures. Test the water if the cause is still unclear. Most orange sink stains have a clear source once you know where to look, and in St. Louis, iron is a common but not the only answer.