A musty, earthy, or damp smell in cold tap water can be unpleasant enough to make you stop drinking from the faucet. In St. Louis, the cause is often something simple near the tap, but it can also come from the water supply itself. Before you buy anything or call anyone, run through the checks below and write down what you notice. That record will help you, and anyone you call later, figure out what to do next.
Start by Noting Where the Smell Shows Up
Pay attention to the pattern before you test anything.
- Is the smell in cold water only, hot water only, or both?
- Does it show up at one faucet or at several throughout the house?
- Does it appear mainly after the water has sat unused for a while, such as after a trip?
- Does it come with cloudy, discolored, or sediment-filled water?
A smell in only one faucet usually points to that fixture or the line leading to it. A smell at every tap, especially cold water, points toward the water source or the main plumbing.
Smell the Water Directly
Fill a clean, clear glass from the cold tap and smell it right away. Then set the glass aside, leave it uncovered for a while, and smell it again. Repeat the same steps with a glass from a different faucet in the house. If the odor is strong at one tap but faint at others, you have a useful clue. Keep the glass out of the sink during these checks so the drain itself does not affect your sense of smell.
Check the Fixture First
Many musty odors start at the faucet, not in the street main. Work through these steps in order:
- Unscrew the aerator at the tip of the faucet and look for slime, grit, or dark material inside.
- Clean the aerator and the faucet opening, then run the cold water for a while and smell it again.
- If the home has a filter on the cold line or under the sink, check whether the cartridge is past its service life and whether the housing has a damp, sour smell of its own.
- Check the drain smell separately. A sewer or rotten odor from the drain is a different problem, and it often means a dry or failed trap rather than a water quality issue.
If cleaning the fixture removes the smell, you have likely found the source.
Look at the Water Itself
Municipal water in St. Louis is treated with a disinfectant, and that disinfectant can leave a noticeable odor on its own. Musty or earthy smells can also come from natural organic material in source water that reacts during treatment or in the distribution system. Those odors can be more noticeable at certain times of year or after changes in treatment, and they can come and go.
Home test kits can help you narrow things down. Useful checks include:
- Disinfectant residual, to see whether the level in your tap looks typical for treated water.
- pH, to see whether the water is unusually acidic or basic.
- Hardness, iron, and copper, since metals can add taste or odor and can also cause staining.
Compare each result against the typical ranges printed on the test kit, and note any result that is clearly outside them. A home test cannot identify every compound, so use it to narrow the question, not to settle it.
Check the Water Provider's Records
Your water provider publishes an annual water quality report, and it is worth reading the most recent one. Look for any notes about treatment changes or maintenance in your area. Then contact the provider directly. Describe the smell, when you first noticed it, which taps are affected, and whether it changes with time. Providers can check distribution conditions near your address and tell you whether other customers have reported similar odors.
Consider a Certified Lab Test
If the smell continues after the fixture checks and home tests, a certified laboratory can run a broader panel that includes metals and organic compounds. Ask the lab for a report that lists each result alongside the standard it is compared to, and ask for help reading it if the terms are unfamiliar. A lab report is most useful when you already have a specific question, such as whether a metal is present at the tap you use for drinking.
When to Get Help
- Contact your water provider promptly if the smell appears at several taps, comes with discolored water, or continues after you clean the fixtures.
- Have a licensed plumber look at the home's plumbing if the odor seems tied to a specific line, a water heater, or a recent repair.
- Talk with a medical professional if you have any concern about drinking the water, especially for infants, older adults, or anyone with a health condition.
In most St. Louis homes, a careful look at the fixture, a few simple checks, and a call to the provider will be enough to point you toward the right next step. Keep your notes, and you will have clear information to work from.