Few household problems are as unpleasant as turning on the tap and getting hit with the stench of rotten eggs. If your water heater smells like rotten eggs, you're smelling hydrogen sulfide gas dissolved in your hot water. It's a common issue, it usually isn't dangerous in the small amounts found in home plumbing, and in most cases it can be fixed. This guide explains what causes the odor, how to tell whether it's coming from your water heater or your water supply, and the practical steps you can take to get rid of it for good.

What Causes the Rotten Egg Smell?

That sulfur odor comes from hydrogen sulfide gas. When people say their hot water heater smells like rotten eggs, they're almost always describing a reaction happening inside the tank or in their water source. Three ingredients usually combine to create the problem:

Sulfate in the water supply. Well water and some municipal supplies contain naturally occurring sulfates.
Sulfate-reducing bacteria. These harmless-but-smelly bacteria thrive in the warm, low-oxygen environment inside a water heater tank. They convert sulfate into hydrogen sulfide gas.
The anode rod. Most tank water heaters use a magnesium or aluminum anode rod to protect the steel tank from rust. The reaction between the rod and certain water chemistries can accelerate hydrogen sulfide production.

The key point is this: the odor is a byproduct of water chemistry and bacteria, not usually a sign your tank is failing. That said, the smell is worth solving because it can make water unpleasant to use and, in rare cases, points to a larger water-quality issue.

Is It the Water Heater or the Water Supply?

The single most useful troubleshooting step is figuring out where the smell is coming from. Run this quick test:

Turn on the cold water tap only and smell it. Then turn on the hot water and smell that.
If only the hot water smells, the problem is almost certainly inside your water heater — bacteria and the anode rod are the likely culprits.
If both hot and cold water smell, the odor is coming from your water source (often a well) and no water heater fix alone will solve it. You'll need water treatment.
If the smell fades after running the water for a minute or two, it points more toward the water heater or a fixture drain; a persistent odor points to the source water.

Don't be fooled by a smelly sink drain, either. Bacteria in a drain trap can produce a similar odor that has nothing to do with your water. Fill a glass with hot water, walk to another room, and smell it there to rule out the drain.

Gas, Electric, Tankless, and RV: Does the Type Matter?

The rotten-egg smell shows up across every kind of system, but the details differ:

Electric water heater smells like rotten eggs: Electric tank models are actually more prone to the odor because they can run at temperatures and conditions that let sulfate-reducing bacteria flourish. The anode rod is usually the first thing to check.
Gas water heater smells like rotten eggs: Gas tanks behave much like electric ones for this issue. One critical caution: natural gas and propane are deliberately given a rotten-egg/sulfur smell so leaks are noticeable. If you smell that odor in the air near the heater — not in the water — leave the area and call your gas utility immediately. That is a potential gas leak, not a water problem.
Tankless water heater smells like rotten eggs: Tankless units heat water on demand and hold very little water, so bacterial buildup is less common. If a tankless system produces the odor, the smell more often traces back to the incoming water supply or nearby fixtures.
RV water heater smells like rotten eggs: RV heaters are notorious for this because water sits in a small tank for long periods between trips. The magnesium anode rod plus stagnant water is a perfect recipe. Draining, sanitizing, and switching the anode rod (or removing it if the manufacturer allows) usually cures it.

Why a New Water Heater Can Smell Too

It surprises a lot of homeowners when a new water heater smells like rotten eggs. You just spent good money on a fresh unit — why the stink? The answer is almost always the anode rod. A brand-new tank has a fresh, highly reactive magnesium anode rod, and if your water has the right chemistry, that reactivity can kick off hydrogen sulfide production quickly.

So if your new hot water heater smells like rotten eggs within days or weeks of installation, it's not a defect and it's not something you did wrong. It's a water-chemistry match with the anode rod. The fixes below apply just as well to new units as to old ones.

Before changing any anode rod, check your warranty. Some manufacturers require the factory anode rod to remain in place, and using the wrong replacement can affect coverage. See what voids a water heater warranty and our warranty guide by brand.

How to Fix the Rotten Egg Smell

When your water heater water smells like rotten eggs, there are several proven approaches. Start with the simplest and escalate as needed.

1. Flush and disinfect the tank

A hydrogen peroxide flush or a chlorine disinfection cycle kills the sulfate-reducing bacteria. This often clears the smell temporarily, but if your water chemistry keeps feeding the bacteria, the odor can return. Turn off power or gas, follow your manufacturer's instructions, and consider having a plumber do this if you're unsure.

2. Replace or change the anode rod

Swapping a magnesium anode rod for an aluminum/zinc or a powered (impressed-current) anode rod is the most reliable long-term fix for many homes. The powered rod doesn't sacrifice metal the way a standard rod does, which eliminates the reaction that produces the odor while still protecting the tank. Learn more about what an anode rod is and how it works.

3. Raise the temperature temporarily

Briefly raising the water heater to a higher temperature can kill bacteria in the tank. Be very careful — hotter water raises the risk of scalding. Read what temperature your water heater should be set to before adjusting it, and return the setting to a safe level afterward.

4. Treat the source water

If both hot and cold water smell, you need to treat the water itself. Options include aeration, activated carbon filters, or oxidizing filtration systems. For well water, a professional water test is the right starting point. The EPA offers general guidance on private well water quality.

When the Smell Points to a Bigger Problem

The rotten-egg odor itself is rarely dangerous, but pay attention if it comes alongside other warning signs:

Discolored water. Rusty or brown water plus odor can indicate tank corrosion. See why your hot water is brown or discolored.
Popping or rumbling noises. Sediment buildup can worsen odor and reduce efficiency. Read about the popping sound your water heater makes.
Inconsistent heating. If you're also short on hot water, check why your water heater isn't producing hot water.
A gas smell in the air. As noted above, this is an emergency — evacuate and call your gas company or 911.

If your heater is aging and the odor is one of several recurring problems, it may be time to weigh a repair-or-replace decision. Knowing your unit's age is the first step — you can check your water heater's age using its serial number, and browse reliability data in our water heater reliability database.

How to Prevent It From Coming Back

Once you've cleared the smell, a little routine care keeps it away:

Flush the tank once or twice a year to remove sediment that feeds bacteria.
Inspect the anode rod periodically and replace it before it's fully consumed. This also helps prevent tank corrosion — see our guide on preventing rust and corrosion.
Don't let water stagnate. For RVs and vacation homes, drain the tank when it will sit unused for long periods.
Consider a powered anode rod if you have persistent odor issues; it addresses the root cause instead of just masking it.

Curious about your specific brand? We have age-lookup and info pages for many manufacturers, including Rheem, Ruud, Reliance, and Marathon. You can also see every manufacturer we support on our brands page.

The Bottom Line

If your water heater smells like rotten eggs, it's usually hydrogen sulfide gas produced by bacteria reacting with the anode rod inside a tank — not a dangerous failure. Start by testing whether only the hot water smells (heater issue) or both hot and cold smell (water-source issue). From there, flushing and disinfecting the tank, swapping the anode rod, and treating source water are the reliable fixes. The one exception you should never ignore is a gas-like sulfur smell in the air near the unit, which means a possible gas leak and calls for immediate action. When in doubt, bring in a licensed plumber to diagnose and treat the problem safely.

Water Heater Smells Like Rotten Eggs? Causes & Fixes