Water Heater Smells Like Rotten Eggs: Causes and Fixes

If your hot water smells like rotten eggs, you don't have a mystery — you have hydrogen sulfide gas in your hot water system. The good news: in nearly every Lawrenceville home, the cause is inside the water heater itself, and the fixes are straightforward. The even better news: the smell usually points at one of just three things, and you can narrow it down in about a minute.

The short answer: a rotten-egg smell from your hot water is almost always caused by sulfate-reducing bacteria living in the tank, or by the tank's magnesium anode rod reacting with sulfur compounds in the water. Run the hot water and the cold water separately — if only the hot water smells, the water heater is the problem. If the cold water smells too, the sulfur is in your water supply.

The 60-Second Test: Is It Your Water Heater or Your Water?

Do this before anything else, because the answer tells you exactly where to aim the fix:

1. Go to a faucet where you've noticed the smell. Fill a glass with cold water only, walk away from the sink, and smell the glass. (Stepping away rules out a dirty drain as the source.)
2. Now run the hot side only into the glass and smell again, away from the sink.
3. Compare:
4. Smell in hot water only? The water heater — or the anode rod inside it — is the source. Keep reading; everything below applies to you.
5. Smell in both hot and cold? The sulfur is in your water supply, and the heater is just warming it. Skip to "When to Call a Plumber" — you'll need a water test or treatment, not a heater fix.

One caveat: a smelly sink drain fools a lot of people. If the glass water doesn't smell but the faucet area does, the problem is bacteria in the drain, not the heater — clean the drain and you're done.

What's Actually Causing the Smell

1. The Magnesium Anode Rod Is Reacting with Sulfur in the Water

Inside every tank water heater is a magnesium or aluminum rod that sacrifices itself to corrosion so the steel tank doesn't rust. GE Appliances confirms that when water contains sulfates, the sulfate can react with the magnesium anode rod — and that reaction produces the rotten-egg smell.

This is the most common cause in Lawrenceville. Most homes here are on Gwinnett County municipal water, which doesn't carry much sulfur on its own — but trace amounts plus a magnesium rod are enough. The smell is usually strongest first thing in the morning (gas builds up overnight) and in heaters that are 2 to 5 years old.

One thing that makes it worse: a water softener. Softened water is more aggressive toward magnesium anode rods, so the reaction — and the smell — intensifies. If the smell started shortly after a softener was installed, this is your likely culprit.

2. Bacteria Living in the Tank

Sulfate-reducing bacteria are everywhere in groundwater and plumbing. They love warm, low-chlorine environments — which is exactly what a water heater is when the thermostat is set low or the tank has been sitting idle. A.O. Smith describes these bacteria as nontoxic to humans; they're a nuisance problem, not a poisoning problem.

This cause is easy to spot: the smell gets worse after the heater sits unused — after a vacation, a guest-bathroom line that rarely runs, or a rental that's been empty. The bacteria feed on sulfur compounds and exhale hydrogen sulfide gas, and the more sediment at the bottom of the tank, the more of them there are. Sediment acts like a buffet.

3. Sulfur in the Water Supply Itself

If your 60-second test found the smell in cold water too, the sulfur is coming from the source. This is the classic well-water problem — sulfur-reducing bacteria or decaying organic matter in groundwater produces hydrogen sulfide before the water ever reaches your house.

Around Lawrenceville this is uncommon on city water, but some homes on the outskirts and in older pockets of Gwinnett County are on private wells, where it's entirely plausible. Source-water sulfur needs water treatment (testing, chlorination, or filtration), not a water-heater repair.

Is It Safe to Shower or Drink?

For hot-water-only smell: generally, yes. A.O. Smith states the bacteria are nontoxic to humans and that hydrogen sulfide is toxic only at extremely high concentrations — concentrations you would smell long before they became harmful. This is a nuisance, not a health emergency.

Two exceptions matter:

• If the cold water smells too, the CDC notes that a change in water smell is sometimes a sign of a real problem. Get the water tested — especially if you're on a well — rather than assuming it's the same nuisance.
• If the smell is in the air, not just the water, stop and think carefully. Natural gas companies add a sulfur-like odorant to gas precisely so leaks are detectable. If you smell rotten eggs near a gas appliance or around the house (not just when running the tap), don't investigate — leave the house and call your gas utility or 911 from outside. Our guide to what to do about smells and other danger signs covers the full emergency checklist.

DIY Fixes That Actually Work (In This Order)

Try these in sequence — each step is slightly more involved than the last, and most odor problems die at step one or two.

1. Flush the Tank

Sediment at the bottom of the tank is where the bacteria live and where minerals react with the anode rod. Flushing it out removes their habitat.

Basic process: shut off power (breaker for electric, gas control to "pilot" for gas) and the cold-water supply, attach a garden hose to the drain valve, run it to a floor drain or outside, open the valve, and drain several gallons — or the full tank if the water runs murky. Open a hot tap inside the house so the tank drains freely, then close everything and refill before restoring power.

If you've never flushed a heater before, our full water heater maintenance guide walks through it step by step, or you can have it done professionally with our sediment flush service. In Lawrenceville's moderately hard water, an annual flush is worth the trouble regardless of smell — it slows corrosion and noise too.

2. Sanitize the Tank with Chlorine

If flushing alone doesn't kill the smell, the bacteria need a stronger answer. GE Appliances lists chlorinating the water heater and all hot water lines as the recommended next step: add household bleach to the tank, fill it, let the chlorinated water sit for a few hours, then flush the whole system until the chlorine smell is gone.

This is an effective fix, but it involves introducing a chemical into your potable system — be precise with the bleach amount and flush thoroughly afterward. If you'd rather not do this yourself, a plumber can do the flush-and-sanitize as a single visit.

3. Temporarily Raise the Thermostat to 140°F

GE also notes that increasing the tank temperature to 140°F can reduce this odor, because the bacteria don't thrive at higher temperatures. A few cautions:

• The U.S. Department of Energy recommends 120°F as the normal setting — 140°F water scalds in seconds. Only raise the temperature temporarily, and consider having temperature-limiting (mixing) valves installed at taps if you run 140°F for more than a day or two.
• Return the thermostat to 120°F once the smell is gone.
• Don't do this on a tank with a failing T&P relief valve or other overheating symptoms.

The Fix Most Homeowners Get Wrong: the Anode Rod

Here's the mistake: "just remove the anode rod." You'll find this advice online, and it does stop the smell — because it removes the reaction partner. But A.O. Smith, Rheem, and Bradford White all say running a tank without an anode voids the warranty, and Rheem adds that it greatly shortens the tank's life. You'd trade a smell for a rusted-out tank. Don't do it.

The right move is to replace the rod with a less reactive type:

• Aluminum-zinc alloy rod ($30–$60 for the part): the standard fix for odor. The zinc suppresses the sulfur reaction while the rod still protects the tank.
• Powered (impressed-current) anode ($150–$300 for the part, $300–$650 installed): uses a small electrical current instead of sacrificial metal. Lasts 10–20 years, essentially eliminates odor permanently, and never needs replacing — but it must stay plugged in to work.

Full pricing, rod types, and the DIY-versus-pro comparison are in our anode rod replacement cost guide: a sacrificial rod swap runs $150–$300 installed or $30–$70 in parts if you do it yourself. Call a plumber for the swap if the old rod is seized (they often are), the heater has low overhead clearance, or the unit is still under warranty — mistakes here are expensive.

When to Call a Plumber Instead of DIYing

Stop troubleshooting and schedule a visit if any of these are true:

• The smell returns after a flush and chlorination — the bacteria or reaction keeps winning, and the anode rod needs professional attention.
• Cold water smells too — you likely need water testing and treatment, not a heater repair.
• The smell started right after a water softener was installed — a pro can switch you to a less reactive rod and re-tune the system in one visit.
• The tank is 10+ years old and the smell comes with rusty water, rumbling, or leaks — you may be nursing a dying tank. See our water heater lifespan guide and the repair-or-replace guide before spending money on odor fixes.
• You're uncomfortable touching gas connections, electrical panels, or plumbing under pressure. That's what plumbers who do this every day are for.

What a Professional Visit Costs

Most rotten-egg odor jobs land in ordinary service-visit territory. From our own cost guides: an anode rod swap runs $150–$300 installed, a powered anode runs $300–$650 installed, and a flush-and-sanitize visit falls in the range of a standard repair call — see our water heater repair cost guide for the full picture.

If the tank itself is finished — 10-plus years old, rusty water, pinhole leaks — no odor fix is worth doing twice. A water heater replacement ends the smell and the problem in one job.

How to Keep the Smell From Coming Back

• Flush the tank annually. Lawrenceville's moderately hard water leaves sediment fast, and sediment is the bacteria's home base.
• Keep the thermostat at 120°F. Turning it lower to save energy creates the lukewarm conditions bacteria love.
• Check the anode rod every 2–3 years (sooner with a softener), and install an aluminum-zinc or powered rod at the first sign of odor.
• After a vacation or long absence: open the hot tap farthest from the heater and let it run for several minutes before using the dishwasher, laundry, or any appliance on the hot water line. Rheem and A.O. Smith both warn that hydrogen gas can accumulate in an idle hot water system — it's extremely flammable, so no smoking or open flames nearby. A sound like air escaping from the pipe as the water starts means the gas is venting; that's expected, just let it finish.

Frequently Asked Questions

Is it safe to shower in water that smells like rotten eggs? Yes, when only the hot water smells. A.O. Smith describes the sulfur bacteria as nontoxic to humans, and hydrogen sulfide becomes toxic only at concentrations far higher than you'd encounter from a water heater. If the cold water smells too, get the supply tested — that's a different situation.

Can I just remove the anode rod to stop the smell? Don't. Removing the rod stops the reaction but leaves the tank unprotected — A.O. Smith, Rheem, and Bradford White all say running without an anode voids the tank warranty and shortens its life. Replace it with an aluminum-zinc or powered anode instead.

Why did the smell start after we came back from vacation? Two weeks or more of sitting idle is ideal for sulfate-reducing bacteria, and hydrogen gas can also collect in the tank. Flush and sanitize the tank, then vent the lines by opening the hot tap farthest from the heater for several minutes before running appliances.

How long does it take to get rid of the smell? A flush takes an hour or two; a chlorination needs the bleach to sit for a few hours plus flushing time. If you go the anode-rod route, the smell usually clears within a day or two of the swap. Recurring smells mean the bacteria are recolonizing — that's a plumber's job.

My cold water smells like rotten eggs too. What should I do? The sulfur is in your water supply, not your heater. Have the water tested (a plumber or water-treatment company can arrange it) and look at chlorination or filtration options. This is common with well water and rare on Lawrenceville's municipal supply.

Rotten-egg hot water is unpleasant, but it's one of the most diagnosable problems a water heater has: hot-only means the tank, both means the supply, and the fixes follow in a clear order. If you've run the test, tried the flush, and the smell won't stay gone — or you'd rather have it handled in a single visit — Water Heater Pros diagnoses and fixes water heater odor across Lawrenceville and Gwinnett County every week. We'll tell you honestly whether you need a flush, a new anode rod, or a new heater.