What Causes Hot Water to Smell Like Rotten Eggs
When your hot water smells like rotten eggs, the cause is almost always hydrogen sulfide gas. In Lake oswego, Oregon, I see this problem in homes on both city and well water. The smell comes from bacteria reacting with sulfur, magnesium, or aluminum inside the water heater. The bacteria thrive in warm, oxygen-poor environments, which is why the odor is strongest in hot water and often absent in cold taps.
I'm Eli, a Certified Water Specialist with over 20 years of experience installing and servicing residential water treatment systems across the United States.
Why It Only Happens in Hot Water
The smell usually appears only in hot water because the water heater creates ideal conditions for sulfur-reducing bacteria. These bacteria feed on the anode rod, a metal component designed to prevent tank corrosion. When the rod corrodes, it releases electrons that bacteria use to convert sulfate into hydrogen sulfide. Cold water doesn't sit long enough or get warm enough to trigger the same reaction, which is why the smell disappears at the cold tap.
In Lake Oswego homes, I've noticed this problem more often in newer water heaters with magnesium or aluminum anode rods. The bacteria colonize quickly, especially if the home has been vacant or the heater hasn't been flushed in a while. Sometimes homeowners think the water itself is contaminated, but the issue is usually isolated to the tank.
Common Fixes That Work and When They Don't
Most homeowners try flushing the water heater or raising the temperature to 140°F for a few hours. Flushing removes sediment and some bacteria, and heat can kill off colonies temporarily. But these fixes don't last if the source of sulfur or bacteria isn't addressed. I've seen the smell return within weeks.
Replacing the anode rod with a powered zinc or aluminum-zinc alloy rod can help. These rods don't feed bacteria the same way magnesium does. But if your water supply has high sulfate levels or sulfur-reducing bacteria, the problem will persist until you treat the water before it enters the heater. That's where oxidation or filtration comes in.
For homes in Lake Oswego dealing with sulfur odor from well water, I usually recommend a system like the WellFusion™ Ultra 64K sulfur removal filter, which uses catalytic media to oxidize hydrogen sulfide before it reaches the tank. For city water with occasional odor, an OZONEX™ ozone generator can provide chemical-free oxidation and disinfection upstream of the heater.
When the Problem Is in the Water Supply
Sometimes the odor isn't coming from the water heater at all. If both hot and cold water smell like sulfur, the source is in the supply line or well. In Lake Oswego, this is more common in rural homes on private wells. Sulfur bacteria can colonize in the well casing, pressure tank, or plumbing, especially if the system hasn't been shocked or maintained.
Testing the water at the well and at the tap helps determine where the bacteria are growing. If sulfate levels are elevated or hydrogen sulfide is detected in the cold water, treatment should happen at the point of entry. I've corrected systems where homeowners replaced three water heaters before realizing the bacteria were upstream the whole time.
For comprehensive well water treatment in Lake Oswego, explore our sulfur removal systems or review our full lineup of well water treatment systems. Both collections include options for oxidation, filtration, and disinfection.
What I Tell Homeowners Before They Buy Anything
Before spending money on a new water heater or treatment system, confirm where the odor is coming from. Run the cold water for two minutes, then smell it. Run the hot water for two minutes, then smell it. If only the hot smells, the issue is likely in the tank. If both smell, treat the supply.
Also check if the odor is worse after the home has been closed up or unused for a few days. That suggests bacterial growth rather than a sulfur contamination problem. In that case, disinfecting the heater and raising the temperature may solve it without filtration.
One thing I've noticed: homeowners in Lake Oswego often assume the problem is unique to their house. It's not. Hydrogen sulfide odor is one of the most common water complaints I handle, and it's almost always fixable once you understand what's feeding the bacteria.
For more guidance on diagnosing and treating odor problems, visit our sulfur odor removal solutions page. If you're unsure what system fits your home, start with our water system quiz for personalized recommendations.
Frequently Asked Questions
Can I fix the rotten egg smell by just flushing my water heater?
Flushing can help temporarily by removing sediment and some bacteria, but if sulfur-reducing bacteria or sulfate levels are present in your water supply, the smell will return. Long-term solutions require treating the water before it enters the heater.
Is the rotten egg smell in hot water dangerous?
Hydrogen sulfide gas is not usually dangerous at the low concentrations found in home water, but it's unpleasant and can corrode plumbing and fixtures over time. If the odor is strong or persistent, it's worth addressing for comfort and system protection.
Why does only my hot water smell and not the cold?
Hot water heaters create warm, low-oxygen environments where sulfur-reducing bacteria thrive. These bacteria react with the anode rod and produce hydrogen sulfide gas. Cold water doesn't sit long enough or get warm enough to trigger the same reaction.
Will replacing the anode rod stop the smell?
Replacing a magnesium anode rod with a powered zinc or aluminum-zinc rod can reduce bacterial activity, but it won't eliminate the problem if your water contains sulfate or sulfur bacteria. Treating the water supply is usually necessary for lasting results.
Do Lake Oswego homes on city water have this problem too?
Yes. While sulfur odor is more common in well water, city water can also develop the smell if sulfur-reducing bacteria colonize inside the water heater. The bacteria feed on the anode rod regardless of the water source.