Turning on the tap and getting a whiff of rotten eggs is unsettling. If your water heater smells like rotten eggs, the culprit is almost always hydrogen sulfide gas in the water, not a problem with your plumbing or a dangerous fuel leak. This guide explains what causes that sulfur smell, how to tell where it's coming from, and the practical steps you can take to clear it up on gas, electric, tankless, and RV water heaters.

The good news: in most cases a rotten-egg odor is a nuisance rather than a health emergency, and it's often fixable. But there's one important exception involving natural gas that we'll cover first, because your safety comes before anything else.

First, Rule Out a Real Gas Leak

Natural gas and propane are naturally odorless. Utilities add a chemical called mercaptan that smells like rotten eggs or sulfur so you can detect leaks. That means a rotten-egg smell can occasionally signal an actual fuel leak rather than smelly water.

Here's how to tell the difference:

Smell only in the water: If the odor appears when you run a hot faucet and disappears otherwise, it's almost certainly hydrogen sulfide in the water, not a gas leak.
Smell in the air near the unit: If you smell rotten eggs in the air around a gas water heater or elsewhere in the home even with no faucet running, treat it as a possible gas leak.

If you suspect a natural gas or propane leak: do not flip switches, light flames, or use your phone indoors. Leave the home and call your gas utility's emergency line or 911 from outside.

For general safety information, the U.S. Consumer Product Safety Commission (cpsc.gov) is a reliable resource. Once you've confirmed the smell is coming from the water and not the air, you can move on to treating the odor.

What Actually Causes the Rotten-Egg Smell in Water

When your water heater water smells like rotten eggs, the odor comes from hydrogen sulfide gas dissolved in the water. This gas is typically produced by a reaction between three things:

Sulfur or sulfate in your water supply — common in well water and some municipal supplies.
Sulfate-reducing bacteria — harmless-to-drink bacteria that thrive in the warm, low-oxygen environment inside a tank.
The magnesium anode rod — the sacrificial metal rod that protects your tank from rust. As it corrodes, it can react with sulfate-reducing bacteria and accelerate hydrogen sulfide production.

This is why the smell is usually strongest in hot water: the warm tank is the perfect breeding ground. If you notice that only the hot side stinks and cold water is fine, you've essentially confirmed the tank is the source.

To understand the anode rod's role, see our explainer on what an anode rod is — it's the single most important component in this whole issue.

Why It Happens on New, Electric, Gas, Tankless, and RV Units

The rotten-egg smell shows up across every type of water heater, but the reasons vary slightly.

New water heater smells like rotten eggs

It surprises many homeowners when a new hot water heater smells like rotten eggs, but it's common. A fresh tank has a brand-new, highly reactive magnesium anode rod. Combined with sulfur-bearing water, it can produce odor quickly — sometimes within days or weeks. This doesn't mean the unit is defective; it means the water chemistry and anode type aren't a good match.

Electric water heater smells like rotten eggs

An electric hot water heater smells like rotten eggs for the same anode-and-bacteria reason. Because electric units often run at slightly lower or more variable temperatures and can have longer periods of standing water, bacteria may grow more easily. If your electric unit is also giving you lukewarm water, a failed heating element could be leaving part of the tank cool enough for bacteria to flourish — a case where checking the elements for continuity with a multimeter can help confirm the root cause.

Gas water heater smells like rotten eggs

A gas water heater smells like rotten eggs from the same water chemistry, but always do the air-versus-water check described above first, since gas odorant smells identical.

Tankless water heater smells like rotten eggs

A tankless water heater smells like rotten eggs less often because there's no standing tank of warm water for bacteria to grow in. When it does happen, the source is usually the incoming water supply itself or sulfur buildup in fixtures and pipes. Descaling the unit and treating the water supply are the usual fixes. If your tankless is acting up in other ways too, our guides on tankless error codes and a tankless that keeps shutting off may help.

RV water heater smells like rotten eggs

An RV water heater smells like rotten eggs frequently, because RV tanks sit unused with warm, stagnant water for long stretches — ideal conditions for sulfate-reducing bacteria. Sanitizing the fresh water system and flushing the heater usually clears it up.

How to Fix a Water Heater That Smells Like Rotten Eggs

Here are the proven approaches, roughly in order of how most homeowners tackle them. Always turn off power (electric) or set a gas unit to "pilot"/"vacation," and let the water cool before working on the tank.

1. Flush and disinfect the tank

Draining, flushing, and sanitizing the tank knocks out the bacteria causing the smell. Many homeowners use a chlorine-based sanitizing procedure, then refill and flush thoroughly. This often gives immediate relief, though the odor can return if the underlying anode/bacteria condition remains.

2. Replace or change the anode rod

Because the magnesium anode is often the biggest contributor, switching to an aluminum/zinc alloy anode rod is one of the most effective long-term fixes for a persistent sulfur smell. Some homeowners with a well-maintained tank consider a powered (impressed-current) anode, which doesn't react the same way. Never simply remove the anode and leave it out — that voids protection and shortens tank life. Check the details in our anode rod guide.

3. Raise the temperature to kill bacteria (carefully)

Bacteria are killed at higher temperatures. Temporarily raising the thermostat can help, but very hot water causes serious scald risk. Review what temperature your water heater should be set to before adjusting, and lower it back to a safe setting afterward.

4. Treat the incoming water

If your whole supply smells (both hot and cold), the problem is your source water, not just the heater. Well-water homes may need aeration, oxidizing filtration, or chlorination. The U.S. Environmental Protection Agency (epa.gov) has guidance on private well water quality.

5. For RVs and tankless units

Sanitize the entire fresh water system for RVs, and descale/flush a tankless unit per the manufacturer's instructions. Treating the water supply prevents the odor from returning.

Preventing the Smell From Coming Back

Once you've cleared the odor, a little maintenance keeps it from returning:

Flush the tank periodically to remove sediment and biofilm.
Inspect the anode rod every few years and replace it before it's fully consumed.
If you're on well water, keep your treatment system serviced.
Consider an alloy anode from the start if you have sulfur-prone water.

Good maintenance also helps prevent related problems like a popping sound from sediment, brown or discolored hot water, and general rust and corrosion. For more troubleshooting, browse our full library of water heater resources and guides.

When Odor Means It's Time to Consider Replacement

A rotten-egg smell alone rarely means you need a new water heater. But if the smell is paired with an old tank, rust-colored water, leaks, or repeated element failures, the unit may be near the end of its life. Age is the biggest factor. If you're not sure how old yours is, you can check your water heater's age by decoding the serial number, or look up your specific brand — for example Rheem, Ruud, Richmond, or Reliance. You can also see the full list of supported brands.

When you're weighing your options, our repair-or-replace guide and the replacement cost calculator can help you decide. And before buying anything, check the warranty guide and what voids a water heater warranty, since changing an anode rod incorrectly can sometimes affect coverage.

Quick Reference: Odor Location vs. Likely Cause

Where you smell it	Most likely cause	First step
Only hot water	Bacteria + anode reaction in tank	Flush/sanitize tank, change anode
Both hot and cold water	Source water (well/municipal)	Test and treat water supply
Air near a gas unit (no faucet running)	Possible gas leak	Leave and call gas utility/911
RV, after sitting unused	Stagnant water bacteria	Sanitize fresh water system
Tankless unit	Source water or scale buildup	Descale and treat supply

If your water heater smells like rotten eggs, start by confirming it's the water and not a gas leak, then flush the tank and address the anode rod. Most homeowners can knock out the odor in an afternoon — and prevent it from coming back with a bit of routine maintenance.

Water Heater Smells Like Rotten Eggs: Causes & Fixes