Hot Water Smells Like Rotten Eggs? Causes and Fixes in Fort Collins
Hot water smells like rotten eggs? Why it happens, how an anode rod swap or chlorination fixes it, and when it is a gas leak.
When only your hot water smells like rotten eggs, the cause is usually hydrogen sulfide gas made inside the water heater, where harmless sulfate-reducing bacteria react with hydrogen from the tank’s magnesium anode rod. The usual fix is to disinfect the tank and swap the anode for a less active one, never to remove it. Fort Collins Water Heater Pros diagnoses smelly hot water and replaces anode rods in Fort Collins, Loveland and across Larimer County.
Call (970) 305-5633 to have smelly hot water diagnosed and your anode rod checked.
Call nowSmell it in the air, not the water? Leave first
If the rotten-egg smell hangs in the air near the water heater, furnace or stove, even with no water running, treat it as a gas leak, and if you are unsure which it is, treat it as gas. Xcel Energy’s safety data sheet describes the odorant added to natural gas as a sulfur smell resembling skunk or rotten eggs, and propane carries an odorant too.
- Get everyone out. Do not light anything, touch electrical switches or use a phone inside, as A.O. Smith’s manual warns.
- Call from outside or a neighbor’s phone. Xcel Energy supplies gas to most of the area, Atmos Energy to Greeley and parts of Windsor, and Black Hills Energy to Wellington; on propane, call your supplier. If you cannot reach them, call the fire department.
- Follow the gas supplier’s instructions before going back in.
Why does my hot water smell like rotten eggs?
It is hydrogen sulfide gas. A.O. Smith’s Signature 100 manual says four things must all be present: sulfate in the water, little or no dissolved oxygen, sulfate-reducing bacteria in the tank, and extra hydrogen from the anode rod’s corrosion-protection reaction.
- Why only the hot side. Rheem’s bulletin on smelly water says these bacteria cannot grow with atmospheric oxygen present, which is why the cold supply often smells fine; in a warm, oxygen-poor tank, the odor appears. People notice it at about 0.5 parts per million, and at 1 to 2 ppm it smells like rotten eggs.
- Why the anode matters. Every glass-lined tank has microscopic bare spots, and the anode, usually magnesium, corrodes in their place. Rheem’s anode bulletin says the more active the anode, the more hydrogen it releases and the more hydrogen sulfide the bacteria can make.
- What raises the odds. State Water Heaters’ service handbook lists water softeners, well water and long stretches with no water use, and says the bacteria thrive below 138°F.
Is it only the hot water? How to find the source
Smell the hot and cold water separately, away from the sink. Fort Collins Utilities suggests filling a clean glass and carrying it to another room, because a smell that disappears away from the sink comes from the drain, not the water.
| Where you notice it | Likely source | What to do |
|---|---|---|
| Hot water only, at every tap | Bacteria and the anode in the water heater | Disinfect the tank; replace the anode |
| One sink, and the glass smells fine elsewhere | Bacteria in the drain or disposal | Clean the drain trap and disposal |
| Hot and cold at every tap, even after running them 2 to 3 minutes | The water supply | Call your water utility; test a private well |
| The air near gas appliances, with no water running | Possible gas leak | Leave and call the gas utility from outside |
| Hot water after the house sat empty for weeks | Still water feeding the bacteria | Run the hot taps; see the vacation question below |
Fort Collins Utilities asks customers to call when every cold faucet smells and running them for two to three minutes does not clear it. On a private well, common around LaPorte, Bellvue and Masonville, have the water tested: Larimer County’s health department supplies sample bottles, collects samples in Fort Collins and Loveland, and lists labs that test well water.
How to fix rotten-egg hot water
Disinfect the tank and hot water lines, then replace the magnesium anode with a less active one. If the smell comes back, a powered anode or continuous treatment of the water supply is the next step.
1. Disinfect the tank with chlorine
Rheem ranks chlorination first, and Bradford White says controlling the bacteria is the only satisfactory way to control the odor. The heat and cold supply are shut off, some water is drained, household bleach goes in through the anode, relief valve or hot outlet opening, and each hot tap is run until it smells of chlorine. After the solution sits, the tank and lines are flushed until the chlorine smell is gone, and the tank is refilled completely before the heat goes back on.
Doses differ by brand: Rheem’s bulletin calls for one gallon of bleach per 30 gallons of tank capacity left for an hour, State’s handbook one gallon per 25 gallons for an hour or more, and Bradford White a half to one gallon left at least three hours, ideally a full day. Follow your own heater’s procedure. State calls chlorination a surface treatment that often has to be repeated, and Rheem says it is fully effective only with a continuous chlorine feeder.
Some guides suggest hydrogen peroxide instead. None of the manufacturer guidance we checked (A.O. Smith, Bradford White, GE, Rheem and State) mentions it, and A.O. Smith warns against chemicals that could contaminate drinking water, so use only a treatment your heater’s manual allows.
2. Water heater anode rod replacement
A.O. Smith says a special zinc anode may help reduce or eliminate the odor, Bradford White that its A420 anode may minimize it, and GE Appliances that a special alloy rod for odor is available for all its heaters; Rheem uses its R-Tech anode, which reduces anode activity. Replacement rods for this job are often sold as aluminum-zinc.
Do it with the chlorination: A.O. Smith’s Signature manual pairs the new anode with chlorinating the tank and all hot water lines. Rheem’s replacement steps use a 1-1/16-inch socket and, in most cases, a long cheater bar to break the seal, and on some heaters, including Rheem’s heat pump and direct-vent models, the anode is not accessible.
HomeAdvisor’s June 17, 2026 repair cost guide puts anode rod replacement at $50 to $150 including labor. Angi’s December 17, 2025 guide puts the part at $20 to $50 and says most plumbers take about an hour.
3. A powered anode if the smell returns
A powered anode protects the tank with a small electric current from a plug-in power supply instead of a metal rod that corrodes away. A.O. Smith sells powered anode kits for some tanks. Ask the manufacturer whether one is approved for your model; GE, for example, says running without an approved anode voids its warranty.
4. Raising the temperature: use care
A.O. Smith says that if the smell is very strong, you could raise the tank to 140°F to reduce bacterial growth, and GE says much the same. Bradford White, though, says sulfur-eating bacteria resist heat up to about 225°F, so a hotter setting may not end the problem. Bradford White also warns that 140°F water can scald within five seconds, and A.O. Smith says mixing valves at each fixture are particularly important above 120°F, the setting DOE recommends.
5. Treat the water supply
If the smell survives a new anode and chlorination, A.O. Smith suggests chlorinating or aerating the water supply itself, and Rheem says a continuous chlorine feeder is the only fully effective fix.
Why you should never just remove the anode rod
Pulling the anode can look like a quick fix, but A.O. Smith says an anode must be installed at all times or the warranty is void, and Bradford White says complete removal “will void the warranty and shorten tank life.” Rheem explains why: without the anode, the bare spots in the glass lining corrode into pinholes and, eventually, a leaking tank, which cannot be repaired.
Water softeners and anode wear
A.O. Smith says a water softener makes the anode wear out faster than normal, so it should be inspected more often. Rheem adds that softened water drastically raises the anode’s current demand and that smelly water is more common in softened water. Local water already measures soft, at 24 mg/L in Loveland’s 2025 report, and Loveland and Longmont say their customers do not need a softener.
When to call a plumber
- The smell returns after chlorination and a new anode
- The anode will not budge, or your heater’s anode is not accessible
- The hot water is rusty, or water appears at the base of the tank
- You would rather not shut off gas, drain and refill the tank yourself
Most tankless water heaters have no anode rod, so a sulfur smell with a tankless unit points more to the water supply or plumbing; tankless units need descaling instead, covered in how to descale a tankless water heater.
Our plumbers replace anode rods, disinfect tanks and give honest repair-or-replace advice; see water heater repair in Fort Collins, or water heater replacement in Fort Collins if the tank itself is failing. For routine care, read our guides to water heater maintenance and how to flush a water heater.
Rotten egg smell FAQ
Is it safe to shower in water that smells like rotten eggs?
Water heater makers describe the bacteria as harmless, and State Water Heaters notes that hydrogen sulfide becomes toxic only at extremely high concentrations, which you would smell long before. If the cold water smells too, or you are on a well, have the water tested.
Why does only my hot water smell like rotten eggs?
Because the gas is made inside the tank, where sulfate-reducing bacteria use hydrogen from the anode rod. Rheem notes the bacteria cannot grow in oxygen-rich cold water.
Will replacing the anode rod stop the smell?
It may, especially paired with chlorination; A.O. Smith says a zinc anode may reduce or eliminate it. Rheem cautions that without continuous chlorination the bacteria can keep growing, so the smell can return.
How much does water heater anode rod replacement cost?
HomeAdvisor’s June 2026 guide puts it at $50 to $150 including labor nationally. Your written, itemized quote gives the real price before any work starts.
Why does my hot water smell worse after a vacation?
Still water helps the bacteria; State lists long periods without water use as a risk. Rheem also warns that flammable hydrogen gas can build up in a hot water system unused for two weeks or more, so run the kitchen hot tap for several minutes before using appliances, with no flame or smoking nearby.
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