Why does my tap water smell like rotten eggs?

Start here: is it the hot tap, the cold tap, or both?

Run each tap on its own before you do anything else. Which taps are affected narrows the cause more than any description of the symptom can.

Hot tap only

Your water heater, not your water

A sulfur smell on the hot tap only is manufactured inside the water heater. The Minnesota Department of Health describes the mechanism precisely: the tank's sacrificial anode is usually magnesium, and it supplies electrons that help convert sulfate already in the water into hydrogen sulfide gas. The cold line never enters the tank, which is why it smells of nothing.

Cold tap only

Hydrogen sulfide arriving through the cold line

A smell on the cold tap means the odor is in the water before it reaches your appliances — dissolved hydrogen sulfide in the supply, or sulfur bacteria growing in the service line or in a branch of your plumbing that is rarely used. A guest bathroom that sits idle for weeks is a classic offender.

Hot and cold

Something upstream of the water heater — or the drain

When hot and cold both smell, the cause sits before the heater: the incoming supply or the service line. Rule out the drain first, though, because it is free to do. Fill a glass, walk away from the sink, and smell it in another room; odor that vanishes was coming from the trap, not the tap.

On a city water supply

On a municipal system the water is disinfected and carries a residual all the way to your meter, so sulfur bacteria thriving in the main is unusual — which is exactly why a sulfur smell at every cold tap is worth a phone call rather than a purchase. Your utility can check the main and your service line, and it wants to know whether a whole street is affected. The number people go looking for is sulfate, and here is the honest position on it: EPA sets sulfate as a secondary standard at 250 mg/L, and secondary standards are not enforceable. EPA states plainly that it does not enforce them and that federal regulations do not require systems to monitor or treat for them. So a sulfate result may simply not exist for your address, and if it does, 250 mg/L is a taste threshold rather than a health limit — Minnesota's health department puts it the same way, noting that above 250 mg/L the water may taste bitter or medicinal. EPA also carries a secondary standard for odor itself, 3 threshold odor numbers, and names rotten-egg among the smells it covers. That is the whole federal apparatus for this symptom: aesthetic, advisory, and frequently unmeasured.

On a private well the causes are different, and we answer that version of the question separately. Read the private-well answer.

What your own utility reports

Enter your ZIP code to see the utility-reported values behind this symptom, taken from the water quality data your system files with regulators. Where your utility reported nothing, this says so rather than filling the gap with an estimate.

What actually fixes it

Most of the time this is not a filter problem, and on a city supply it usually is not even a water problem. If the smell is hot-water-only, the fix is at the water heater. Minnesota's health department lists three: swap the magnesium anode for one made of a different material such as aluminum, disinfect the tank with chlorine bleach, or raise the thermostat to 160 degrees Fahrenheit for several hours to kill the bacteria — the last of which needs care, because water at that temperature scalds and the thermostat must be turned back down afterwards. An anode is a water-heater part and costs a small fraction of any filtration system. Note what a whole-house filter cannot do here: it sits upstream of the heater, and the odor is created downstream of it. If both taps smell, call your utility before you buy anything, because what arrives at your meter is theirs to fix and no equipment you own changes it.

When it is worth testing

The cold tap smells as well as the hot tap.
Ask your utility for the most recent sulfate result for your service area — and expect that it may not have one, since sulfate monitoring is voluntary. If nothing recent exists, have a certified lab run sulfate and hydrogen sulfide on a cold-tap sample. Minnesota's health department notes that activated carbon handles hydrogen sulfide below about 1 mg/L and oxidizing media up to roughly 6 mg/L, so the measured level, not the strength of the smell, is what decides the equipment.
The smell arrived suddenly and the water also looks or tastes different.
A certified-lab panel on a cold-tap sample covering sulfate plus general bacteriological quality, so a change in the water is separated from a change in your plumbing. Minnesota's health department is direct that in most cases a rotten-egg smell does not relate to the sanitary quality of the water — but it also notes the rare case where the gas comes from sewage or other pollution, and a bacteriological result is what tells those apart.
The smell is chemical, solvent-like or petroleum rather than sulfurous.
This is not the same problem and it does not belong on this page. Stop drinking the water, stop using it for cooking, and call your utility and your state or local health department the same day. A fuel or solvent odor points at contamination reaching the supply, and that is investigated by the people with the authority to sample the system, not settled by a home filter.

Frequently asked questions

Is tap water that smells like rotten eggs safe to drink?

The smell alone does not answer that, which is the honest starting point. Hydrogen sulfide is detectable by nose at levels far below where it becomes a health question, so a strong smell is not evidence of a strong concentration. Minnesota's health department states that in most cases the rotten-egg smell does not relate to the sanitary quality of the water. What the smell does tell you is where to look: hot-tap-only points at your water heater, and a smell on the cold tap points at the water itself and is worth reporting to your utility.

Why does only my hot water smell like rotten eggs?

Because the odor is made in the water heater rather than delivered by it. The sacrificial anode that protects the tank from corroding is usually magnesium, and according to Minnesota's health department it supplies electrons that help convert sulfate in the water into hydrogen sulfide gas. Replacing that anode with one of a different material, disinfecting the tank, or raising the tank temperature for several hours are the three standard responses, and none of them says anything about the quality of the water arriving at your house.

Will a water filter get rid of the rotten-egg smell?

Only if the smell is in the water, and on a municipal supply it often is not. A whole-house filter is plumbed in before the water heater, so it cannot remove an odor the heater is producing after it. Where hydrogen sulfide really is in the incoming water, Minnesota's health department puts activated carbon at levels below about 1 mg/L and oxidizing media filtration up to about 6 mg/L — which means you need a measurement before you can choose sensibly. Work out which side of the meter the problem is on first.

Why does my utility have no sulfate number for my address?

Because it is not required to have one. Sulfate is a secondary standard, set at 250 mg/L on taste grounds, and EPA states that it does not enforce secondary standards and that federal regulations do not require water systems to monitor or treat for them. Many systems test anyway and publish the result; many do not. When the lookup on this page tells you sulfate is not reported for your utility, that is the real answer rather than a gap in our data, and the way to change it is to ask your utility directly.

Other tap water symptoms

Sources

U.S. EPA — Secondary Drinking Water Standards: Guidance for Nuisance Chemicals — retrieved 2026-07-27
Minnesota Department of Health — Hydrogen Sulfide and Sulfur Bacteria in Water — retrieved 2026-07-27
Minnesota Department of Health — Sulfate in Water — retrieved 2026-07-27

All tap water problems by symptom

By TapWaterData Team