A rotten egg smell from the hot tap is one of the more unsettling things a homeowner in St. Peters can notice. It is also one of the more useful clues, because the odor often points to the water heater rather than the water supply itself. This guide covers what usually causes it, what to check first, and when to bring in a licensed plumber.
Why the smell shows up at the hot tap
Most storage water heaters contain a sacrificial anode rod, a metal rod that corrodes so the steel tank does not. Common rod metals include magnesium, aluminum, and zinc. In some tanks, bacteria can react with the rod and with sulfate dissolved in the water, producing hydrogen sulfide gas. That gas is what gives the water its sulfur or rotten egg odor. Magnesium rods are often the ones linked to this problem, although the odor can appear with other rod types too.
St. Peters tap water is described as hard in public water reports, and many homes here run a softener that swaps hardness minerals for sodium. Changes in water chemistry, including after a softener is installed or its settings are changed, can affect how a tank behaves over time. Treat that as a pattern to watch for rather than a sure cause.
Confirm where the smell comes from
Before opening any equipment, sort out whether the smell belongs to the hot side alone. Run the cold tap at a bathroom sink, then check the hot tap at the same sink. If only the hot side smells, the water heater or its plumbing is the likely source. If both sides smell, look at the water supply, a softener, a well system, or the drains instead.
- Smell the cold tap and the hot tap at the same sink, one after the other.
- Check a second fixture, such as the bathtub or kitchen sink, since one fixture can be misleading.
- Note whether the smell is strongest at the start of a draw and fades after the water runs for a while.
- Note whether the smell started after a softener was installed, repaired, or re-timed.
- Compare any drain or sewer odor, which smells different and usually comes from pipes rather than the heater.
Inspect the anode rod
Before you open anything, switch the heater off at the power switch or gas control and let the water cool. Shut off the water supply to the heater. Gas-fired units need extra care, so if you are unsure about the gas valve, stop and call a professional. Hot water can scald, and a tank under pressure can release water when opened, so relieve pressure carefully and follow the manufacturer's instructions.
Once the top fitting is accessible, remove the rod and look at it. A rod in reasonable shape has an even layer of corrosion along its length. A worn rod shows heavy pitting, large bare patches, or a thin remaining core that looks close to bare wire. A rod that is mostly consumed is due for replacement. A replacement should match the tank's thread size and fit the space above the tank, so check the length before buying, since a rod that is too short may not seat properly.
Flush the tank
Loose sediment at the bottom of the tank can hold odor-causing material and can make the problem look worse than it is. Drain the tank through the bottom valve into a bucket or an outdoor drain until the water runs clear. Sanitizing a tank with chemicals is a different job. That work is better left to a licensed plumber, who can match the product and procedure to the system.
Recheck after the work
After the rod and tank work, run hot water normally for several days and recheck the hot tap at the same sink where you first noticed the smell. If the odor is gone, keep the rod on a regular inspection schedule. If it returns, the next step is usually a professional look at the tank, the rod, and any water chemistry changes made since the smell started.
When to call a licensed plumber
- The smell persists after the rod has been checked and the tank flushed.
- The tank shows leaks, rust at the seams, or a relief valve that keeps dripping.
- The heater is gas-fired and you smell gas rather than a sulfur odor. Leave the house, call your gas utility from outside, and do not operate switches.
- You are not comfortable working on the tank, its controls, or its fittings.
A simple order of operations
- Confirm the smell is on the hot side only.
- Inspect the anode rod and replace it if it is mostly consumed.
- Flush the tank until the water runs clear.
- Recheck the hot tap after several days of normal use.
- Call a licensed plumber if the odor returns or any warning sign appears.
A water heater problem can look like a water quality problem, and the reverse is also true. Working through the steps in order helps a St. Peters homeowner tell the two apart without guessing.