Sulfur smell in city water

Best for

Homes on a public water system that notice a sulfur or rotten-egg smell at the tap.

Wrong fit

If you're on a private well, the causes and fixes are different, so start with the main rotten-egg smell page.

Tradeoff

Most city-water sulfur smells are cheap to fix, but you have to find which one you have, and the utility won't work on plumbing inside your home.

City water is a different problem

A public water system treats and disinfects its water and is required to monitor it. A rotten-egg smell in the supply itself does happen. Washington’s Department of Health says that, although rare there, municipal water as well as private well water can contain hydrogen sulfide, and USGS notes the gas forms mostly as groundwater moves through organic matter or minerals such as pyrite. So systems that draw from wells are the ones most likely to see it.

But most sulfur smells on city water start in the house. Tucson Water says rotten-egg, musty or sewer smells are most commonly caused by bacteria growing in a sink drain or water heater. So before you buy anything or call anyone, spend five minutes finding where the smell starts. The smell diagnosis tool on the homepage asks the same questions as the steps below.

Step 1: hot or cold?

Run the cold water at the kitchen sink, then the hot. Then do the same at a bathroom sink.

• Hot only: the water heater is making the gas. Grand Prairie, Texas explains that the factory-installed magnesium rod in a water heater can turn dissolved sulfur compounds into the gas you smell at the faucet.
• Cold and hot: the smell is in the water before it reaches the heater, either from the supply or from bacteria in your home’s plumbing. Grand Prairie notes outdoor faucets usually carry cold water only, so a clean-smelling outdoor faucet suggests the cold supply is fine.

UGA Extension adds a useful rule: if the smell goes away after the water runs for a few minutes, the problem is probably in the household plumbing. If it stays, the source may be the water supply.

Step 2: one sink, or every sink?

If only one sink smells, suspect the drain. The gas rises from the drain opening while the water runs, so it seems to come from the tap.

The glass test, from Tucson Water and UGA Extension:

1. Fill a clean glass with cold water at the smelly sink.
2. Walk away from the sink.
3. Swirl the water and smell it.

If the water in the glass doesn’t smell, the drain or garbage disposal is the source, and the water is fine.

Fixing a drain smell

Tucson Water’s method: pour 1/2 cup of bleach mixed with 1/2 cup of water down the drain, wait 20 minutes, then flush with water. If your home is on a septic tank rather than city sewer, Tucson says to use 1/2 cup of baking soda with 1/2 cup of water instead of bleach. If the smell keeps coming back, remove the sink trap, clear out any buildup, and reinstall it.

Tucson notes these smells can be worst in hot summer months, and when a sink or shower hasn’t been used for a while.

Fixing a water heater smell

City water carries ordinary amounts of sulfate, and the heater does the rest. Grand Prairie’s advice to customers:

• Flush it. Run hot water at all fixtures until it runs cold. You may need to repeat this periodically.
• Heat it first. You can raise the heater temperature for several hours before flushing, but watch for scalding at the taps and turn it back down afterward.
• Swap the anode. A plumber can replace the magnesium rod with an aluminum rod.

Tucson and UGA Extension add that heaters left unused, turned off for a while, or set at a low temperature are more prone to odor. The full set of fixes, including aluminum-zinc and powered anodes, is on hot water smells like rotten eggs.

When the cold water smells everywhere

If the cold water smells at every tap and doesn’t clear after running, either the supply has an odor or bacteria are growing in your home’s plumbing.

Call the utility first. Washington’s Department of Health says to contact your water system if the tap water smells like rotten eggs, and that its contact information is on your water bill. Tucson Water, for example, asks customers with continuing odor problems to call its water quality support team. The utility can tell you whether others nearby have reported the smell and whether its water is the source.

Ask about the source. Your utility’s annual water quality report, the Consumer Confidence Report, tells you where your water comes from. EPA’s CCR page has a tool for finding yours. If your city draws from groundwater, an occasional sulfur odor in the supply is more plausible.

If the utility’s water is fine, the bacteria are probably in your plumbing. Grand Prairie says a smell in the cold water or on both sides may come from sulfur-reducing bacteria in the pipes, and a qualified plumber may need to disinfect the home’s water system with a chlorine solution and flush it. City staff can’t enter your home or work on your plumbing, but Grand Prairie notes they can discuss the problem and suggest ways to reduce the odor.

After a vacation, a move or an empty house

Sulfur smells often show up after water has sat still. Tucson Water says bacteria tend to grow when faucets go unused or the hot water has been off, and UGA Extension says heaters left unused or turned off for a long time are more likely to smell. A home that sat empty before you moved in, a guest bathroom nobody uses, or a house you’ve just come back to after two weeks away are all classic cases.

What to do:

1. Run every cold tap for a few minutes, then every hot tap, including tubs and showers you rarely use. This replaces stale water in the pipes.
2. If only the hot water still smells, flush the water heater the way Grand Prairie describes, by running the hot water at all fixtures until it runs cold.
3. Pour Tucson’s bleach-and-water mix down any drain that still smells, wait 20 minutes, and flush.
4. If a smell lasts after that, work through the hot-or-cold and one-sink-or-all steps above.

For a rental, tell the landlord. The water heater and the plumbing are usually theirs to fix.

Telling smells apart

Tucson says a chlorine-like taste and smell may come from elevated chlorine, and suggests chilling an open container of water in the refrigerator overnight. USGS describes earthy and musty smells as coming from natural organic compounds in surface water. EPA’s secondary standard for odor is 3 threshold odor number (TON), and EPA’s table lists “rotten-egg” among the odors it covers. Secondary standards are guidelines that EPA doesn’t enforce.

Do you need a filter?

Usually not. A drain or water heater smell doesn’t need a filter at all, and if the supply smells, the utility is responsible for it. A carbon filter at the kitchen tap can help with taste while the utility investigates.

A whole-house sulfur system built for well water is rarely needed on city water. If you’re thinking about one, confirm with the utility that the smell is in the supply and persistent, and test it, before spending the money. If you’re actually on a private well, see why water smells like rotten eggs, and for health questions see is sulfur water safe.