Why Does My Water Smell Like Rotten Eggs?
A rotten-egg or sulfur smell is almost always hydrogen sulfide gas. If only the hot water smells, the water heater is the usual source; if the cold water smells too, it is coming from the water supply, most often groundwater from a private well. A one-minute tap check tells you which.
Where does it smell?
Run the hot tap, then the cold tap, at more than one sink. One choice gives you the likely source and what to do.
All five cases as a list
- Only the hot water smellsUsually points to: The water heater: its magnesium anode rod can turn natural sulfate in the water into hydrogen sulfide.What to do: Ask a plumber about replacing the anode rod (aluminum-zinc or powered anodes are common swaps). Check the heater's warranty before removing anything.
- The cold water smells, the hot does notUsually points to: Hydrogen sulfide in the water coming into the home. Heating can drive the gas off, so hot water may smell less.What to do: On city water, call your utility. On a well, have the water tested by a certified lab.
- Every tap smells, hot and coldUsually points to: The water supply rather than one fixture or the heater.What to do: On city water, call your utility and say when it started. On a well, test the water.
- Only one sink smellsUsually points to: Often the drain, not the water: bacteria in the drain trap release the same smell.What to do: Fill a glass, step away from the sink and smell the water. If the glass is fine, clean the drain.
- The smell fades after the water runs a minuteUsually points to: Water that sat in the pipes or the heater overnight.What to do: Usually a nuisance. If it keeps coming back, follow the hot-or-cold rows above.
Three nuisances, one worth testing
- Nuisance: changes look, smell or taste
Hydrogen sulfide in groundwater
Every tap smells, especially cold water, and the home is on a private well. Sulfur bacteria and some rock types (for example shale and sandstone) produce the gas.
- Nuisance: changes look, smell or taste
The water heater's anode rod
Only the hot water smells. The magnesium rod that protects the tank from corrosion reacts with sulfate in the water.
- Nuisance: changes look, smell or taste
A drain, not the water
One sink only, and a glass of water carried to another room has no smell.
- Worth testing
High sulfate (mostly wells)
The water also tastes bitter or medicinal. At high levels sulfate can have a laxative effect, especially for people not used to the water. EPA's guidance level for taste is 250 mg/L.
When to call your utility
- Call your utility if every tap smells, the smell started suddenly, or it came with a notice from the utility.
- Say whether the smell is in hot, cold or both, which taps, and when it started.
- Your utility's phone number and website are on your city or utility page here: search your address, city or ZIP below.
On a private well, no utility tests your water. Sulfur smells are most common in wells, and a certified lab can test for hydrogen sulfide and sulfate; your state's health department lists accredited labs. Private well water by state and county.
Frequently asked
- Penn State Extension, “Hydrogen Sulfide (Rotten Egg Odor) in Water Wells”
- Minnesota Department of Health, “Sulfate in Well Water”
- US EPA, “Secondary Drinking Water Standards: Guidance for Nuisance Chemicals”
Reviewed October 7, 2026 by the PurityMap Editorial Team. Prepared with AI assistance. General information, not medical advice. Your utility's records describe the water system, not the water at your tap. Health disclaimer · Spot a mistake? Send a correction.
Why does only my hot water smell like rotten eggs?
The water heater is the usual cause. Its magnesium anode rod can react with natural sulfate in the water to make hydrogen sulfide. A plumber can replace the rod with a different type; check the heater's warranty first.
Can I drink water that smells like rotten eggs?
It depends on the cause. Hydrogen sulfide at the levels that cause a smell is mainly a nuisance, but on a well the smell is a reason to test, because a lab test also shows what else is in the water. On city water, call your utility.
Will a filter remove the sulfur smell?
Small amounts can be handled by activated carbon, but well water with a strong smell usually needs whole-home treatment such as aeration or oxidation and filtration. Test the water first so the treatment matches the level.