Why Does Your Hot Water Smell Like Rotten Eggs?

If only your hot water smells like rotten eggs, the cause is usually a reaction inside the water heater. Penn State Extension explains that tank water heaters are fitted with a magnesium rod to slow corrosion, and that this rod can chemically reduce sulfates in the water to form hydrogen sulfide, the gas behind the rotten egg odor. If both hot and cold water smell, the source is more likely the water supply itself.

The usual quick fix has a catch that many guides leave out. Penn State Extension says removing the magnesium rod often stops the smell, but that removal could increase corrosion, shorten the life of the water heater, and will likely void the manufacturer's warranty. Its recommended fix is replacing the magnesium rod with an aluminum rod, which should eliminate the odor while keeping corrosion protection in place. The same extension guide notes a less common trigger: in rare cases, water treatment equipment such as a water softener can create conditions for sulfur-reducing bacteria and hydrogen sulfide. This post covers how to pin down the source, what the anode rod does, and how to fix the smell without cutting your water heater's life short.

What Causes the Rotten Egg Smell in Hot Water?

The smell is hydrogen sulfide gas. Penn State Extension describes it as the gas that gives water a distinctive rotten egg odor, and notes that people can smell it at very low levels, well below 0.5 milligrams per liter.

In a water heater, the reaction usually involves the anode rod. Water heater manufacturer A.O. Smith explains that a sacrificial anode rod made of aluminum, magnesium, or zinc is installed in steel water heaters to attract damaging elements in the water, corroding over time so the tank does not. When that rod is magnesium, Penn State Extension says it can convert naturally occurring sulfates in the water into hydrogen sulfide.

Is It the Water Heater or the Water Supply?

Run a simple test at a sink:

1. Run cold water and smell it.

2. Run hot water and smell it.

3. Compare the two.

If the odor is only in the hot water, Penn State Extension points to the water heater as the likely source. If both hot and cold water smell, the problem is more likely in the water supply. On a private well, that calls for a water test through a state-accredited lab, which Penn State Extension says you can find through the Pennsylvania Department of Environmental Protection. On public water, contact your water utility.

Is Rotten Egg Smell From a Water Heater Dangerous?

Usually it is a nuisance rather than a health threat. Penn State Extension says hydrogen sulfide in water is an aesthetic concern and has no drinking water standard, because it makes water undrinkable by taste and smell long before it reaches harmful levels.

It can still cause other problems. The same guide notes hydrogen sulfide can corrode metal plumbing and leave yellow or black stains on fixtures and inside pipes.

When the Smell Is Not the Water

A rotten egg smell in the air near a gas water heater or furnace is a different emergency. Trane and Lennox both link that smell to a possible gas leak. If you smell it near a gas appliance rather than in the water, leave the house and call your gas company from outside.

How Do You Get Rid of the Smell?

The fix depends on the source. For a water heater, the options from Penn State Extension and A.O. Smith are:

• Replace the magnesium anode with an aluminum rod. Penn State Extension says this should eliminate the odor while keeping corrosion protection.

• Do not simply remove the anode. Penn State Extension warns that running without it could increase corrosion, shorten the heater's life, and likely void the warranty.

• Have the anode inspected regularly. A.O. Smith recommends checking the anode rod once a year, and says how long it lasts depends on the chemicals in the water, how much hot water you use, and whether a water softener is installed.

• Keep up with flushing. Rheem recommends flushing a tank once a year for most homes and every six months where water is hard, to clear sediment.

For well water that smells on both taps, Penn State Extension describes whole-house treatment options such as chlorination with filtration, oxidizing filters, and activated carbon, chosen based on the measured hydrogen sulfide level.

Should You Replace the Anode Rod Yourself?

A.O. Smith's anode check starts by turning off the power or gas and the cold water supply, then draining a few gallons from the tank. Its maintenance guide recommends gloves and eye protection for any water heater work and advises calling a professional if you are not comfortable working with gas or electricity.

There is also a practical reason to have a plumber look: an anode check shows how much protection the tank has left. If the rod is badly depleted on an older heater, that is useful information for deciding between a repair and a replacement. Our guide on how long a water heater lasts before replacing covers age and warning signs, and when to schedule water heater repair in Pittsburgh lists the symptoms that should not wait.

Can a Water Softener Cause Rotten Egg Smell?

It can, though Penn State Extension describes it as rare. The extension guide says adding water treatment equipment like a softener may create a favorable environment for sulfur-reducing bacteria to grow, which can produce hydrogen sulfide.

A.O. Smith also notes that a water softener affects how long an anode rod lasts. If the smell started around the time a softener was installed, mention that to your plumber, since it narrows down the cause.

If you are replacing an old tank anyway, it may be worth comparing options. Our guide to tank vs tankless water heaters for Pittsburgh homes covers the differences, and gas water heater owners dealing with other issues can read about a water heater pilot light that keeps going out.

FAQ

Why does only my hot water smell like sulfur?

Penn State Extension explains that a magnesium anode rod in the water heater can react with sulfates in the water to produce hydrogen sulfide, which is why the smell shows up only on the hot side.

Is it safe to shower in water that smells like rotten eggs?

Penn State Extension treats hydrogen sulfide in water as an aesthetic concern, noting people can smell it well before it reaches harmful levels. If the smell is in the air near a gas appliance, leave and call your gas company.

Can I just remove the anode rod?

Penn State Extension advises against it. Removal can increase corrosion, shorten the water heater's life, and will likely void the warranty.

What anode rod stops the rotten egg smell?

Penn State Extension says replacing the magnesium rod with an aluminum rod should eliminate the odor while maintaining corrosion protection.

How often should an anode rod be checked?

A.O. Smith recommends inspecting it once a year.

Does a rotten egg smell mean my water heater is failing?

Not necessarily. Penn State Extension ties the smell to anode rod chemistry, not tank failure. Still, have the rod inspected, since A.O. Smith says the anode is what protects the tank from corrosion.

Water Heater Service in Bethel Park and the South Hills

All Pro Plumbing Heating & Cooling services tank and tankless water heaters from all major brands, from diagnosis and repair to replacement and routine annual maintenance, and it also installs and maintains water softeners and filtration systems. John Oakes, a Registered Master Plumber, started the company as a home-based family business in 2006, and it now runs from its own office on Library Road in Bethel Park with 10 local employees. You get clear pricing and options before any work begins. See water heater repair and replacement and tank and tankless water heater service.

Visit All Pro Plumbing or call 412-595-8204 today. Contact us for more information.