If your St. Louis home has water that smells or tastes off only at the hot tap, the cause is often between the water heater and the faucet, not in the main supply. Cold water from the same line may be fine. That split is the first useful clue, and this guide walks through what to check before you call anyone.
Start by comparing hot and cold
Run the cold tap for a minute, then smell and taste a sample. Repeat at the hot tap using the same routine. If only the hot side has the odor, the source is most likely in the water heater tank, the hot line, or the fixtures on that side. If both sides smell the same, the issue is more likely in the supply, which points back to the city main or, for a private well, to the well itself.
Write down what you notice. A rotten egg smell, a metallic taste, or a dull, sour odor each points to different suspects, so describe it in plain words rather than trying to match it to a label. Note whether the smell is strongest at the first draw in the morning or after the tap has run for a while.
Common reasons hot water changes
Warm water speeds up many chemical and biological reactions, so the heater is a frequent place where small problems become noticeable. A few possibilities come up often in homes across St. Louis:
- Sediment settling at the bottom of the tank, which can carry a dull or gritty taste and sometimes causes popping or rumbling when the heater runs.
- A sacrificial anode rod that is wearing down, which can release a metallic or odd taste in some tanks.
- Sulfur-producing bacteria in the tank or hot lines, which can cause a rotten egg smell that shows up mostly on the hot side.
- Dissolved gases that come out of solution more readily in warm water, so an odor that was faint in the cold line can be easier to notice at the hot tap.
Simple checks you can do yourself
Before you open any drain or touch the heater, turn off the power or gas supply to the unit and let the water cool, since hot water can scald. Then work through these steps in order.
- Compare the hot and cold taps at the same sink, using the same run time, and write down which one has the odor.
- Check the tank drain valve. Attach a garden hose, open the valve, and let a small amount of water run into a bucket or outside. Cloudy water, grit, or dark flakes point toward sediment.
- Inspect the cold inlet and the hot outlet fittings for crusting, corrosion, or drips.
- Find the heater's age and any paperwork in your files. Older tanks are more likely to need service, and that changes how you weigh repair against replacement.
When to test rather than guess
If the smell is clearly rotten egg and it returns after the tank has been checked, a lab can test the water for sulfide and bacterial activity. Ask the lab about sampling from the hot tap, and collect a cold sample at the same time so you can compare the two. Use the same collection method both times and label each bottle with the tap and the time. A lab report tells you what is present in the water, but it does not identify the cause on its own, so read the results alongside what you saw in the tank.
Working with a licensed plumber
A licensed plumber can inspect the heater, the anode rod, and the fittings, then tell you whether the tank can be cleaned, the anode replaced, or the unit replaced. Ask what they found, what they changed, and whether they retested the hot side afterward. Keep your own notes so you can tell whether the smell comes back.
What to watch over the next few weeks
Note whether the odor returns after you drain or service the tank. A smell that stays on the hot side only, after the basic checks are done, is a reason to retest rather than keep changing things at random. The age of your heater and the pipes in your home both matter, so record those details with your notes. A clear pattern in your log will make any future conversation with a plumber or a lab much more productive.