A cold tap that smells musty or tastes flat after a week away is one of the most common water complaints in St. Louis homes, and it is usually a plumbing question before it is a water quality question. Water that sits in a pipe nobody uses for days changes. This guide covers what is happening, what to do first, and when the problem is worth a closer look.
Why Water Goes Stale in Certain Taps
Water leaving the treatment plant carries a small amount of disinfectant, and that residual keeps working as water moves through the street mains and into your service line. Once water sits still inside a pipe for a long stretch, the disinfectant fades, and the water picks up whatever the pipe material and the air contribute. Guest bathrooms, basement utility sinks, outdoor hose bibs, and taps at the far end of a long branch are the usual places. Many older houses across St. Louis City and St. Louis County have long branch runs, so a seldom-used line can hold water longer than most homeowners expect.
Step One: Find Out Which Taps Are Affected
Before you change anything, sort out the pattern. Ask yourself these questions:
- Does only one faucet smell, or does the whole house?
- Is the problem on the hot side, the cold side, or both?
- Did it start after a trip or a stretch when nobody was home?
- Did it start on a specific day, which could point to nearby street or main work?
Step Two: Flush the Line
Flushing moves the stale water out and pulls fresh water from the main into the branch. Work through it in this order:
- Open the affected cold tap fully and let it run until the water feels steadily cold, then keep it running a little longer.
- Run the matching hot tap the same way if the hot side is also affected.
- Run a nearby tap, such as a kitchen sink, so fresh water reaches the branch from the other direction.
- Fill a clean glass from the flushed tap and smell it. Repeat if the odor is still there.
Unscrew the screen at the tip of the faucet, rinse it, and check for grit or slime. Aerators are a common place for sediment and biological film to collect, and a clean screen often clears up a complaint on its own. Flushing uses water, so treat it as a deliberate step rather than something you do in the background.
Step Three: Check the Hot Water Side Separately
If only the hot tap smells, the water heater is a more likely cause than the street supply. Sediment and bacteria in the tank, along with a reacting anode rod, can produce odors that show up only on hot water. Do not treat this as a thermostat problem and change the setting without reading the manufacturer guidance for your heater. Check the age of the unit, look for any service records, and have a licensed plumber inspect the tank if the smell persists.
What the Smell Might Point To
Homeowners describe odors in different words, and those words help narrow the cause. Plain descriptions:
- A chlorine smell, similar to a swimming pool: usually the disinfectant residual, which fades in a line that sits.
- A musty or earthy smell: often biological growth in a little-used line or fixture.
- A rotten egg smell: commonly hydrogen sulfide, which can come from the water heater or from groundwater. If you have a private well, this needs its own testing path.
- A metallic taste: can come from metal pipe or fittings, so note which tap it is.
When to Test
Flushing and a clean aerator solve most stale water cases. If the odor persists after a full flush at every affected tap, or the water looks discolored, it is time to collect a sample. A state-certified laboratory can run the tests you need. Ask the lab about lead sampling if your home has older plumbing, since that is a separate test from a general water panel. Keep a short written note with the date, the tap, what you noticed, and what you did, so you can tell a pattern from a one-time event.
If neighbors on your street report the same change, contact your water provider. They can tell you whether there was recent main work or a valve operation in the area.
Simple Habits That Prevent It
- Run seldom-used taps briefly once a week when you are home.
- Before a long trip, plan to flush the guest and basement taps again when you return.
- Keep aerators clean so sediment does not build up where you cannot see it.
- Write down changes as they happen so they are easy to compare later.
For most St. Louis homeowners, a stale tap is a flushing task, not an emergency. Work through the steps in order, note what changes, and move to testing only when the pattern stays the same after a full flush.