A sudden change in how your St. Louis tap water smells or tastes is worth a few minutes of sorting before you call anyone. The most useful first question is not what the water is like, but where the change shows up. One faucet, hot water only, or the whole house each point to a different cause, and each cause has a different next step.

Start with the pattern

Before you touch anything, note three things: which fixtures show the change, whether it is hot, cold or both, and when it started. Write them down. A short log is more useful than memory when you talk to a plumber or your water provider.

  • Only one tap: suspect that fixture first, including its aerator screen, supply valve and the trap under the sink.
  • Hot water only: suspect the water heater rather than the city supply.
  • Every cold tap in the house: check the supply side, any treatment equipment, and whether there has been recent work nearby.
  • Outdoor spigot tastes normal but indoor taps do not: look at the plumbing, filters and fixtures inside the home.

Check the fixture and the drain

Unscrew the aerator at the tip of the faucet and look for grit, flakes or slime. Rinse it, then run the tap for a minute. Next, check the drain. Odors that seem to come from the tap are sometimes coming from a dry trap or a slow drain with built-up residue. Run a cup of water down the suspect drain, then smell the basin. If the odor is strongest at the drain, the water supply may not be the source.

Look at the water heater if the smell is hot-only

A rotten-egg or sulfur-like smell that appears only on hot water often comes from the water heater rather than the street. Certain bacteria can grow in a tank, and some tank parts can react with the water and produce a sulfur smell. Compare hot and cold at the same sink. If only the hot side smells, call a licensed plumber to inspect the tank and anode rod. Do not treat this as a supply problem until the water heater has been ruled out.

If the smell is strong and resembles natural gas, leave the home, avoid anything that could create a spark, and call your gas utility or the emergency number from outside. This is a safety step, not a water test.

Check treatment equipment in the home

Any treatment device in your St. Louis home can change taste and smell when it is overdue for service or has recently been changed. Carbon filters can release odors when they are old, and a water conditioner or softener may have been adjusted or reloaded. Check the dates on filter cartridges. If your unit has a bypass, compare water from a tap before and after the equipment to see whether the change starts there. Keep the manufacturer's service records with your log.

Ask the water provider the right questions

Water systems in the St. Louis area sometimes do flushing, repairs or treatment adjustments, and those changes can briefly alter taste or odor. Call your water provider and ask whether there have been recent main repairs, flushing or treatment changes in your area, and whether any notices have been posted. Give them your address, the date the change started, and which fixtures are affected. Ask whether they can check water at or near your service connection.

Test before you decide

A simple home check helps. Fill a clean, clear glass from a cold tap and smell it. Then run the cold tap for a few minutes, fill another glass, and compare. Taste a small sip only if the water looks clear and the smell is mild. Never taste water that smells of gas or strong chemicals. If the water is discolored, cloudy or gritty, stop and call before using it. If you are on a private well, a laboratory that tests drinking water can tell you what is present, and you should keep the result sheets with your log.

When to call for help

  1. Call a plumber if only hot water has the odor, or if a trap or drain looks like the likely source.
  2. Call your water provider if every cold tap in your home changed at the same time.
  3. Call a laboratory if you are on a private well and want to know what is in the water.
  4. Call your gas utility or emergency services right away if the smell resembles gas.