A rotten egg smell from the hot tap is one of the more unsettling things a homeowner can notice, and it is also one of the easier problems to narrow down if you know where to look. In St. Louis homes, the cause is often in the water heater rather than the pipes or the city supply. This guide walks through the checks in a sensible order so you know what to do next.
Start by Comparing Hot and Cold
Before touching anything, run the cold tap in the kitchen or a bathroom for a while, then do the same with the hot tap. If the smell shows up only on the hot side, the problem is most likely inside your home, usually in the water heater or the hot water piping. If both sides smell, the issue is more likely in the water itself, so the service line or the municipal supply becomes the question. Note which side the smell comes from, and whether it is strong at the first draw or only after the water has been sitting.
What the Smell Usually Means
The rotten egg odor is most often linked to hydrogen sulfide, a gas that can form when certain bacteria act on sulfate in water in an environment with little oxygen. Water heaters are a common place for this to happen because they hold warm water for long periods. The smell alone does not tell you whether water is safe to drink, so do not diagnose it by nose alone. If you have questions about drinking water, a lab test is the way to find out, and your water provider can explain what they test for.
Checks You Can Make at Home
- Look at the water heater and confirm the tank is in service and that its power or gas supply is working normally.
- If the tank has a drain valve, run a little water from it to see whether the smell is present at the source.
- Find the anode rod access point near the top of the tank. Its condition affects how the tank handles corrosion, and this is a point to bring up with a licensed plumber rather than something to fix yourself.
- Run only the cold side of each fixture to confirm whether the smell is limited to the hot line.
Sorting Out the Anode Rod
The anode rod is a sacrificial metal rod designed to draw corrosion away from the tank lining. Over time it wears down, and in some homes a worn rod is linked to odor problems. Checking one means draining part of the tank and pulling the rod, which is a job many homeowners leave to a plumber. If you do the inspection yourself, shut off power or gas, close the cold supply, and drain only as far as needed. Replacing the rod is a decision to make after you know its condition.
Things That Are Not the Answer
Adding chemicals to the tank, raising the heater setting to try to clear the smell, or flushing the tank without a plan can make the problem harder to read or hide the evidence you need. Avoid pouring bleach or drain cleaner into the hot side as a test. Also avoid assuming the problem is the drain. A drain odor usually smells different and shows up at sinks regardless of which tap you run, so it is a separate issue from hot water odor.
When to Call for Help
Call a licensed plumber if the smell persists after you have checked both sides of the system, if the tank is leaking, or if the water heater is old or making unusual noises. A plumber can test the tank, inspect the anode rod, and judge whether flushing or a rod change makes sense. If the smell appears in both hot and cold water across the whole house, contact your water provider in St. Louis and ask what they have recorded for your area. Keep notes about when the smell appears, which fixtures are affected, and whether it changed after recent work on the home.
Keeping Track Over Time
A simple log helps. Write down the date, which tap you ran, how long it ran, and what the smell was like. Patterns often show up quickly. A smell that appears only after a trip or a long stretch without use points toward water sitting in the tank or lines. A smell that comes and goes with the seasons may point to changes in the supply. Bring that log to a plumber or water provider, and it will shorten the conversation.