If your St. Louis tap water runs clear when you fill a glass in the kitchen, but turns orange, brownish or metallic only from the hot side, the problem may not be the water coming into your house at all. Hot water can pick up rust and sediment from the water heater itself, and that changes how you should troubleshoot. This guide walks through how to tell the difference before you spend money on equipment you may not need.

Why hot water can look different from cold

Water heaters are steel or lined tanks that stay warm, and warm water speeds up corrosion inside them. Over time, rust flakes and mineral deposits settle on the bottom of the tank. When you draw hot water, some of that material can be stirred up and carried into your fixtures. Iron that is already in the supply can also show up more noticeably on the hot side, so the two sources can overlap.

That is why a rusty hot tap alone does not tell you whether the iron came from your supply line, your water heater, or both. You need to compare hot and cold water side by side.

Compare the cold and hot taps first

  1. Choose a kitchen or utility sink tap that is close to the water heater and is not connected to a filter or softener, if you have one.
  2. Let the cold water run until it is steady, then fill a clear glass and look at it in good light.
  3. Switch to hot, let it run until it is steady, then fill a second clear glass.
  4. Compare the two. Cloudiness or color only in the hot water points toward the heater or its piping. Color in both points toward the supply, or to both sources.
  5. Repeat the check at a second tap elsewhere in the house so you can see whether the problem is local or whole-house.

Look at the water heater

If the hot side is the problem, the tank is the next suspect. Most tanks have a drain valve near the bottom. Attach a garden hose and drain a small amount into a bucket outdoors, watching what comes out. Rust-colored water that clears over time suggests loose sediment. Grit that keeps coming back, a metallic taste, or a rotten smell can mean something else, so note what you see rather than guessing.

Be careful with the drain valve. Water in the tank can be very hot, and a valve that has not been opened in a long time may leak or stick. If the valve will not close fully or the water is scalding, stop and ask a licensed plumber to handle it.

Testing the water for iron

Home test strips and kits can show whether iron is present, but they usually give only a rough result and may not separate hot from cold. A certified laboratory report gives a clearer picture. When you request a test, ask for both the cold supply and the hot water results, and tell the lab where each sample came from. Collect samples only as the lab instructs, since a sample taken from the wrong tap, or after the water has sat in the pipes for a long time, can give misleading results.

Most public water systems publish a yearly quality report. If you are on St. Louis city water, that report can show what was measured in the supply. It describes the water entering your home, not the condition of the tank or the pipes inside it, so use it to compare results rather than as a replacement for testing.

Signs the problem is inside the house

  • Only hot water is discolored, and the color improves after you drain the heater.
  • Sediment shows up in the bottom of the tank each time you drain it.
  • Stains appear in the tub or sink only on the hot side.
  • The water heater is old, and no one in the household knows whether it has ever been flushed.

Signs the problem is in the supply

  • Both hot and cold taps show color when first opened in the morning.
  • Several fixtures across the house show the same staining.
  • Neighbors on the same street report similar water.

When to get help

Call a licensed plumber if the water heater drain valve leaks, if the tank is old or sits on a leaking base, or if you cannot tell where the discoloration begins. If your home has a private well, the water is your responsibility from the wellhead onward, so a well contractor or water treatment professional who tests the source is a sensible next step. Homes across St. Louis and the surrounding area differ, and the right fix depends on where the iron comes from, not on the color alone.