Rotten-egg smell, rusty or cloudy hot water

First, find out if it’s hot water only

Smell and color problems are commonly blamed on the water heater, but often the heater only makes an existing water problem easier to notice. The quickest way to tell is to compare taps. The Vermont Department of Health suggests checking after you’ve been away from home for a few hours, because your sense of smell dulls quickly.

1. 01

   Run the cold tap, then the hot tap, at the same sink

   Fill a clear glass from each. Smell each one away from the sink, and look at the color against something white.

2. 02

   Note whether it fades

   Does the smell or color clear after the water runs for a minute or two, or stay the same?

3. 03

   Check another fixture

   One faucet or the whole house? If you have a softener, compare softened and unsoftened taps (an outdoor spigot is often unsoftened).

Rotten-egg smell from the hot tap: bacteria and the anode

The smell is hydrogen sulfide gas. Rheem says people can detect it at about 0.5 parts per million: below 1 ppm it smells musty, and at 1–2 ppm it smells like rotten eggs. Rheem calls it “a water chemistry condition, rather than a water heater problem,” but the heater is where the chemistry happens.

Most tanks carry a magnesium anode rod, a sacrificial metal bar that corrodes so the steel tank doesn’t (see anode rods). As it works, it releases hydrogen. Harmless sulfate-reducing bacteria, which A.O. Smith says often get into a water system during construction or through a break in underground piping, use that hydrogen to turn sulfate into hydrogen sulfide. A.O. Smith says water softeners, well water and long periods without water use all raise the odds, and Rheem says the problem is more common in softened water.

Fixes, in the order manufacturers suggest them

1. Disinfect the tank and plumbing (shock chlorination). A.O. Smith calls this the simplest treatment but a surface treatment that often needs repeating. Vermont’s health department warns the smell can return within a few weeks if any bacteria survive.
2. Replace the anode with a less active one. Rheem’s fix is a bleach flush plus its R-Tech anode, which reduces anode activity, and it says this “may not be 100% effective.” Vermont and Minnesota health officials suggest asking a dealer about an anode of a different material, such as aluminum. Powered (electronic) anodes are also sold as odor fixes; those claims come from sellers.
3. Treat the water supply. Rheem says a continuous chlorine feeder is the only fix that is 100% effective. A.O. Smith lists continuous chlorination or aeration of the supply as longer-lasting solutions.

A.O. Smith notes that because the bacteria come with the water, odor treatment isn’t a warranty repair, so expect to pay for the visit. For anode prices, see what a new anode costs.

Smell from every tap: well water and hydrogen sulfide

If the cold water smells too, the heater isn’t the source. Minnesota’s Department of Health says hydrogen sulfide can occur naturally from decay and reactions with soil and rock, come from sulfur bacteria in the groundwater, well or plumbing, or rarely from pollution. EPA notes that private wells aren’t regulated under the Safe Drinking Water Act, so testing and treatment are up to the owner.

• Health: both states say the bacteria aren’t harmful, but hydrogen sulfide gas in the air can be hazardous at high levels, so it should be vented and not allowed to collect in well pits, basements or well houses.
• Test more than the smell: the rotten-egg odor usually isn’t a sign of unsafe water, but in rare cases it comes from sewage or other pollution, so both states advise testing for total coliform bacteria and nitrate.
• Bacteria in the well or plumbing: shock chlorination of the well and plumbing, which may require a licensed well contractor.
• Hydrogen sulfide in the groundwater: Vermont lists activated carbon for low levels (under about 1 mg/L), an oxidizing filter such as manganese greensand up to about 6 mg/L, and chemical oxidation plus filtration above that.

Rusty or brown hot water: tank, iron bacteria or pipes

Rusty-looking water is usually iron. EPA’s secondary drinking water guideline for iron is 0.3 mg/L, above which water can take on a rusty color, sediment and a metallic taste. Manganese above 0.05 mg/L causes black to brown water and black staining. These are aesthetic limits, not health limits.

Hot water only

Three causes are common, and they need different responses.

• Iron bacteria. A.O. Smith says these, not tank failure, are the most common cause of rusty hot water. They feed on dissolved iron and thrive where soluble iron exceeds 0.2 ppm, in low-oxygen water below 138°F. Softeners, well water and long idle periods help them. Treatment is shock chlorination, and A.O. Smith says the tank usually needs a new anode because the bacteria speed anode failure.
• Sediment. Loose rust-colored sediment can collect at the bottom of a tank. A flush may clear it; see how to flush a tank water heater.
• Tank corrosion. Rheem says brown or reddish hot water often points to corrosion inside the tank or a worn-out anode, and ENERGY STAR lists rust in the water as a sign the heater’s interior is breaking down.

Hot and cold

The City of Albany, Oregon’s water department says the most common cause of brown, red, orange or yellow water is rusting galvanized steel pipe inside the home. It puts their typical life at about 20 years before corrosion shows, up to 40 for well-made pipe. Signs it’s your plumbing: water is discolored on first use in the morning, clears after running a few minutes, and may show at some faucets but not others. The permanent fix is replacing the pipe, and when copper is joined to old steel, a dielectric fitting keeps the copper from making the steel rust faster.

Cloudy or milky water: air or minerals

Water holds dissolved air, and the air can come out as tiny bubbles that make it look milky. Albany’s water department says milky white water “is almost always caused by air,” and says it may be more noticeable with seasonal temperature changes or after the water has been shut off and turned back on.

1. 01

   Do the glass test

   Fill a clear glass and set it down. If the cloudiness is air, it clears from the bottom up within a few minutes (City of Albany; East Valley Water District).

2. 02

   Air: nothing to fix

   Both utilities say water that clears this way is safe. If it doesn’t clear after about five minutes, Albany suggests calling the utility.

3. 03

   Grit or flakes that settle: minerals

   White particles that sink are likely scale. USGS explains that heating hard water forms solid calcium carbonate deposits in a water heater. Flushing removes loose material; the long-term answer is in hard water and your water heater.

When it means the heater needs replacing

Smell and air problems almost never mean a new heater. Rust is different. Rheem says some discoloration can be fixed with maintenance or a new anode, but “persistent problems usually suggest your water heater is nearing the end of its lifespan,” and once a tank is corroding from the inside, replacement “becomes the only safe and cost-effective solution.”

If you’re weighing a repair against a new heater, repair or replace walks through the numbers. Installed prices from Home Depot’s published ranges run $1,600–$2,400 for a tank.

Sources

Sources checked October 5, 2026. Prices, codes and rebates change. Check current details with your installer and local permit office.

1. Hydrogen sulfide in drinking water (updated Mar. 17, 2025) ↗ · Vermont Department of Health
2. Hydrogen sulfide and sulfur bacteria in well water (updated Oct. 18, 2024) ↗ · Minnesota Department of Health
3. Secondary drinking water standards: guidance for nuisance chemicals ↗ · U.S. EPA
4. Private drinking water wells ↗ · U.S. EPA
5. Technical Bulletin 22: Smelly water ↗ · A.O. Smith
6. Technical Bulletin 21: Discolored water ↗ · A.O. Smith
7. Technical Bulletin 23: Chlorination procedure ↗ · A.O. Smith
8. Signature 100 gas water heater installation instructions and use & care guide (100341468, 2021) ↗ · A.O. Smith
9. Technical Service Bulletin 1206: Smelly water and the rotten egg odor ↗ · Rheem
10. 5 signs your water heater is going bad (Dec. 22, 2025) ↗ · Rheem
11. When should you replace your water heater? ↗ · ENERGY STAR
12. Water FAQ (discolored, cloudy and smelly water) ↗ · City of Albany, Oregon, Public Works
13. Cloudy water? ↗ · East Valley Water District (California)
14. Hardness of water ↗ · U.S. Geological Survey
15. Water heater installation cost guide ↗ · Home Depot