Why your hot water smells bad and what you can do to fix it

That rotten egg smell coming from your hot water most likely isn’t your imagination. A sulfur-like odor is a common problem, especially when the smell only appears when you turn on the hot tap. In many cases, the source is inside the water heater, where bacteria, minerals, or internal components react as the water heats up. While the smell is unpleasant, it’s usually tied to a specific cause that can be addressed with the right maintenance or repair.

What causes a sulfur smell in hot water?

A rotten egg or sulfur smell in hot water almost always comes from hydrogen sulfide gas. This gas forms when sulfur reacts with bacteria or metal inside the water heater. Cold water can contain the same elements, but heating the water speeds up chemical reactions and releases the odor more strongly, which is why the smell is usually worse, or only noticeable, when you run hot water.

The source of the odor typically falls into one of three categories: bacteria inside the water heater, a reaction involving the anode rod, or sulfur already present in the water supply.

Bacteria inside the water heater

Sulfur-reducing bacteria can grow inside a water heater tank, especially when the water sits unused for periods of time. These bacteria thrive in warm, low-oxygen environments and feed on naturally occurring sulfur compounds in the water.

As the bacteria break down those compounds, they produce hydrogen sulfide gas, which creates the rotten egg smell. Because this process happens inside the tank, the odor usually comes from hot water taps only, not cold ones.

The anode rod reacting inside the water heater

The anode rod is a metal rod installed inside the water heater to protect the tank from corrosion. It does its job by corroding instead of the tank itself.

In certain water conditions, especially water with high sulfate content, the anode rod can react with sulfur and bacteria inside the tank. This reaction produces hydrogen sulfide gas, leading to a sulfur smell in the hot water. This issue is more common with magnesium anode rods and tends to show up even in otherwise clean water.

Sulfur in your water supply

In some cases, the smell starts in the water itself. Sulfur can naturally occur in groundwater, which is why this problem is more common with well water than municipal water supplies.

When sulfur is already present in the source water, heating it releases the odor more quickly and intensely. If you notice a sulfur smell in both hot and cold water, or if the odor is present throughout the home, the issue may be coming from the water supply rather than the water heater alone.

How to get rid of rotten egg smells in hot water

Getting rid of a sulfur smell usually means addressing what’s happening inside the water heater, although in some cases the issue starts with the water itself. These fixes are listed from simplest to more involved, and many homeowners find relief after just one step.

Flush and clean the water heater

Draining and flushing the water heater tank can help when odor-causing sediment or bacteria have built up inside. Over time, minerals and debris settle at the bottom of the heater, creating an environment where sulfur-reducing bacteria can thrive.

Flushing removes loose sediment and refreshes the water inside the tank. This can reduce or eliminate mild odors, especially if the smell is recent or only noticeable after the heater has been sitting unused. For persistent smells, flushing is often a short-term improvement rather than a permanent fix, but it’s still a good first step before moving on to other solutions.

Replace or upgrade the anode rod

Replacing the anode rod is one of the most effective ways to eliminate sulfur smells coming from hot water. If the odor is strong, persistent, and limited to hot taps, the anode rod is often the main contributor.

Some anode materials are more likely to react with sulfur in the water. Switching to an aluminum or zinc-aluminum anode rod can significantly reduce or stop the chemical reaction that produces hydrogen sulfide gas. This fix addresses the source of the smell rather than masking it, which is why it’s often a long-term solution.

Disinfect the water heater

Disinfecting the water heater can help when sulfur-reducing bacteria are clearly the cause. This is more common in homes with well water, water heaters set to lower temperatures, or systems that sit unused for extended periods.

Disinfection temporarily kills bacteria inside the tank and plumbing, which can eliminate odors for weeks or months. If the smell returns after disinfection, it usually means the conditions that allow bacteria to grow are still present. In those cases, replacing the anode rod or addressing the water supply may be more effective.

Address sulfur in the water supply

If the sulfur smell is present in both hot and cold water, or returns quickly after heater-related fixes, the issue may be coming from the water itself. Sulfur in the source water will continue to release odors no matter how clean the water heater is.

In these situations, filtration or water treatment may be necessary to remove sulfur before it enters the home. Treating the water supply prevents odors at every tap and protects the water heater from recurring sulfur-related problems, making it the most complete solution when sulfur is present in the incoming water.

A sulfur or rotten egg smell in hot water is unpleasant, but it’s usually fixable without replacing the entire water heater. In many cases, the solution comes down to cleaning the tank, replacing the anode rod, or addressing sulfur in the water supply. If you want to dig deeper into diagnosing issues or handling repairs yourself, our DIY water heater repair help walks through common problems, replacement parts, and step-by-step fixes.

Taking care of the odor early can prevent bigger issues later and keep your hot water smelling clean and fresh.

Frequently asked questions about sulfur-smelling hot water

Why does my hot water smell but cold water doesn’t?

When only the hot water smells, the source is usually inside the water heater. Heating water can intensify sulfur odors, especially when sulfur-reducing bacteria or an anode rod reaction is involved. Cold water doesn’t trigger the same reaction, so the smell stays confined to hot taps.

Why does the smell come and go?

Sulfur smells can fluctuate based on water usage, temperature, and how long water sits in the tank. The odor may be stronger first thing in the morning, after the heater hasn’t been used, or when hot water demand is low. Changes in water chemistry or seasonal shifts in water supply can also affect how noticeable the smell is.

Is the rotten egg smell dangerous?

In most homes, a sulfur smell in hot water is not dangerous and is mainly a nuisance. The odor usually comes from hydrogen sulfide gas at very low levels. However, if the smell is extremely strong, persistent throughout the home, or accompanied by other gas odors, it’s a good idea to stop using the water and have the system checked to rule out other issues.

Does a water heater need to be replaced because of sulfur smells?

In most cases, no. Sulfur odors are typically caused by bacteria, anode rod reactions, or sulfur in the water supply, not a failing tank. Replacing or upgrading the anode rod and cleaning the heater often resolves the problem. Full replacement is usually only necessary if the heater is already near the end of its lifespan or has other major issues.

Will raising the water temperature fix the smell?

Raising the water temperature can slow bacterial growth and sometimes reduce odors, but it’s rarely a permanent fix. Higher temperatures also increase the risk of scalding and energy use. It’s usually better to address the root cause, such as the anode rod or sulfur content, rather than relying on temperature alone.