Why Your Water Heater Smells Like Rotten Eggs and How to Fix It

You turn on the hot water and the bathroom fills with a smell like rotten eggs. It's unpleasant, but it's also one of the more fixable water heater problems. In most homes the cause is a reaction inside the tank, and it can be cleared up without replacing anything major.

What causes the smell

That odor is hydrogen sulfide gas. In a water heater, it usually comes from harmless sulfate-reducing bacteria reacting with the tank's anode rod. The anode rod is a metal rod, usually magnesium or aluminum, that corrodes on purpose so your steel tank doesn't. When those bacteria meet a magnesium rod in warm water, they produce hydrogen sulfide, and you smell it at the tap.

A few things make it more likely:

• Well water, which is common in the outlying parts of Hamilton, Boone and Hendricks County and more likely to carry sulfates and bacteria

• A water softener, which can speed up the reaction with a magnesium rod

• Water that sits unused, like in a vacation home or a guest bath that rarely runs

• A low temperature setting that lets bacteria thrive

Heater or water supply? A quick test

Run cold water at a sink for a minute and smell it. Then run hot water at the same sink.

• Only the hot water smells: the problem is inside your water heater.

• Hot and cold both smell: the sulfur is coming from your water source, most often a well. The water heater may be making it worse, but it isn't the root cause.

If you're on city water and both taps smell, call your water provider. If you're on a well, a water test will show what you're dealing with.

How to fix it

Swap the anode rod

This is the fix that works in most homes. Replacing a magnesium rod with an aluminum-zinc rod cuts down the reaction that creates the gas. Another option is a powered anode, which protects the tank with a small electrical current instead of a metal rod that wears away. Powered anodes are a good choice for well homes with stubborn odor problems.

Anode rods are tightened in hard and sit under the top of the tank, so it helps to have clearance above the heater and the right tools. Don't just pull the rod out and leave it out. The smell goes away, but the tank loses its corrosion protection and can rust through much sooner. It can also affect the manufacturer's warranty.

Flush and disinfect the tank

If bacteria have built up, the tank should be flushed and sanitized. That usually means shutting off power or gas, draining the tank, adding a hydrogen peroxide solution, letting it sit, then flushing and refilling. Follow the heater manufacturer's instructions or have a plumber do it, since the tank and water can be very hot and the power or gas has to be handled safely.

Check the temperature

Settings well below 120°F give bacteria an easier time. Keeping the heater around 120°F is a good balance for comfort, energy use and scald safety.

Treat the water if you have a well

If both hot and cold smell, treating the water where it enters the house is the long-term fix. Depending on your test, that could be filtration, an aeration or oxidizing system, or well disinfection.

When replacement makes more sense

If the heater is old, already showing rust or leaks, or the smell keeps coming back after a new rod and a proper cleaning, replacing the heater may be the better value. We'll explain why if that's the case. We install Bradford White tank heaters and Navien tankless units, and right now you can take $50 off a tank installation or $500 off a tankless installation.

When to call us

If you'd like the anode rod swapped and the tank sanitized in one visit, give us a call. We'll figure out whether the smell is coming from the heater or the water supply and give you options and a price before any work starts. Learn more about our water heater repair service, or our water filtration options for well homes.

FAQ

Is the rotten egg smell dangerous?

At the low levels found in hot water, it's usually a nuisance rather than a health risk. It can tarnish fixtures and silverware over time. If you smell rotten eggs near a gas appliance rather than at the tap, treat it as a possible gas leak: leave the house and call your gas utility or 911.

Why did the smell start after I got a water softener?

Softened water can make a magnesium anode rod react faster, which produces more hydrogen sulfide. Switching to an aluminum-zinc or powered anode usually solves it while keeping the benefits of soft water.

How quickly does the smell go away after the fix?

Once the rod is replaced and the tank is flushed, the smell typically fades within a day or two as fresh water cycles through.

Can the smell come back?

It can if the water chemistry stays the same and the heater still has a magnesium rod, or if water sits unused for long periods. A yearly flush and the right anode rod keep it from returning.

Should I just remove the anode rod?

No. Without an anode, the steel tank corrodes much faster and can start leaking years early. Replace it with a rod designed to reduce odor instead.

Tired of smelly hot water? Call or text (317) 731-3028, or visit our water heater service page.