Why does my hot water smell like rotten eggs?

What that rotten egg smell actually is

You're smelling hydrogen sulfide gas dissolved in your hot water. It's produced inside the tank when sulfate-reducing bacteria meet the sacrificial anode rod.

The anode is a metal rod (usually magnesium) that corrodes on purpose so your steel tank doesn't. When bacteria are present, that corrosion reaction throws off hydrogen sulfide, which is the source of the smell.

The good news: this is one of the more fixable water heater complaints. Most homeowners solve it themselves for $20–$100 in parts.

The key diagnostic question is simple. Does only the hot water smell, or does the cold smell too?

Why it's happening in your tank

In nearly every hot-only case, the culprit chain is the same: sulfate-reducing bacteria plus a magnesium anode rod plus warm, still water.

The bacteria are usually already in the water supply at low levels. The tank gives them a warm, oxygen-poor home to multiply. The magnesium anode gives them the chemistry they need to make hydrogen sulfide.

That's why the standard fix attacks all three: change the anode metal, disinfect to kill the bacteria, and raise the temperature to keep them down.

A few things make it worse. Well water tends to carry more of these bacteria than treated city water. A water softener can push the chemistry toward smell production.

And low usage is a big one. A tank that sits (guest bathroom, vacation property, a house on the market) grows bacteria far faster than one flushed with fresh water daily.

How to fix it, step by step

This is a real DIY job, but it involves a pressurized, hot tank. Take it slow and kill the power first.

Start by confirming the diagnosis. Smell the cold water. If it's clean and only hot stinks, you're in the right place.

Turn off power at the breaker for an electric heater, or set the gas control valve to pilot. Then shut the cold water inlet valve on top of the tank.

Open a hot tap somewhere in the house to relieve pressure. Hook a hose to the drain valve and drain a few gallons to check for sediment.

Now find the anode rod. It's usually under a plastic cap or a hex head on top of the tank. You'll need a 1 1/16 inch socket and a breaker bar; these get torqued in tight.

Pull the old rod and look at it. A magnesium rod eaten down to a thin wire or steel core confirms the cause. Install an aluminum-zinc alloy rod or a powered anode in its place.

Before you refill, disinfect. Pour in hydrogen peroxide (a pint or two of 3%) through the anode port, or do a chlorine shock. Refill, then run every hot tap until you smell the treatment come through, and let it sit an hour.

Flush it all out, restore power, and set the thermostat to 140 for 24 hours to finish off the bacteria. Then dial it back to 120 for safety and efficiency.

• 1 1/16 inch socket and a long breaker bar for the anode nut
• Aluminum-zinc anode rod or powered anode
• Garden hose for draining
• 3% hydrogen peroxide or unscented chlorine bleach for disinfection
• Teflon tape for the new anode threads

What it costs in 2026

DIY is cheap. An aluminum-zinc anode rod runs $25 to $45. Hydrogen peroxide or bleach is a few bucks. Call it $20–$100 all in, depending on whether you already own the socket and breaker bar.

A powered anode is the pricier DIY option at $130 to $180, but it's a permanent fix for stubborn recurring smells and it lasts the life of the tank.

If you hire a plumber to swap the anode and disinfect, expect $200–$800 depending on your area and how hard the old anode is to remove.

Where costs climb: source-water sulfur. Whole-house treatment (aeration, chlorine injection, or a catalytic carbon filter) runs $1,500 to $4,000 installed. That's only relevant if your cold water also smells.

• Aluminum-zinc anode rod: $25 to $45
• Powered anode: $130 to $180
• Disinfection supplies: $5 to $15
• Plumber anode swap and flush: $200–$800
• Whole-house sulfur treatment (source water only): $1,500 to $4,000

DIY or call a pro?

Most people can handle the anode swap and disinfection. If you're comfortable draining a tank and swinging a breaker bar, go for it.

Call a plumber when the anode nut is seized on an older tank, when you can't safely access the top of the heater, or when the smell keeps returning after you've done everything right.

Recurring smell after a proper fix points to either a stubborn bacteria source or sulfur in the source water. That's when a water treatment pro earns their fee, because they can test the water and size the right system.

One honest note: if your heater is 12 or more years old and starting to leak or rumble, spending on repairs to chase a smell may not be worth it. Weigh the fix against replacement.

Can you live with it for a while?

The smell isn't a safety emergency, so you won't be forced to act tonight. But waiting isn't free.

Every week the magnesium anode keeps corroding, and the bacteria colony keeps growing. Both make the eventual fix harder and shorten your tank's life.

If you're going to wait, at least bump the thermostat to 140 for a day to knock the bacteria back and take the edge off the smell. Set it back to 120 afterward.

Don't wait months. A neglected anode can disappear entirely, leaving your steel tank unprotected and rusting from the inside.

Safety before you start

Two big risks with this job: dry-firing an electric element and scalding yourself.

Always cut power at the breaker before you drain an electric heater. An exposed element that fires without water burns out in seconds and can be a shock hazard.

The water in the tank is hot enough to scald instantly. Let it cool, drain carefully, and keep kids and pets away from the hose discharge.

Ventilate the room. Hydrogen sulfide is flammable at high concentration, and you don't want to breathe a lot of it in a closed closet.

Well water vs city water

This matters more than most people realize. Well water is far more likely to carry sulfate-reducing bacteria and dissolved sulfur straight from the ground.

On city water, the anode swap and disinfection almost always solves it, because the utility's chlorine keeps bacteria levels low to begin with.

On well water, the same fix works but may not hold as long. That's the classic case for going straight to an aluminum-zinc or powered anode instead of trying magnesium again.

If you're on a well and even the cold water smells, get a water test. You're likely looking at whole-house treatment, and the anode is a side issue.

How we diagnose this

We work the cheapest, most likely cause first and rule out the source before touching the heater.

Step one is always the cold-water sniff test, because it splits every case into two very different paths.

From there we inspect the anode, because a corroded magnesium rod confirms the diagnosis and tells us how aggressive the water is.

We recommend the anode swap and disinfection before any talk of powered anodes or treatment systems, because it solves the majority of cases for under $100. We only escalate when the smell proves it needs escalating.