Why Your Water Heater Smells Like Rotten Eggs – And How to Fix It

A hot shower shouldn’t come with an unpleasant surprise, but if your water smells like rotten eggs, there’s a problem lurking in your water heater. That sulfur-like odor isn’t just a nuisance—it’s a sign of underlying issues that need attention. Understanding why this happens is the first step toward restoring clean, fresh-smelling hot water in your home. The good news is, there are solutions. At Gold Star Plumbing & Drain, we’ve helped countless homeowners tackle this problem with professional water heater repair in Tempe, AZ.

The Science Behind the Rotten Egg Smell

That foul odor comes from hydrogen sulfide gas, which forms under specific conditions inside the water heater. The most common culprit is a chemical reaction between the tank’s anode rod and naturally occurring bacteria in the water supply. The anode rod, typically made of magnesium or aluminum, is designed to prevent corrosion inside the tank. When certain bacteria interact with the metal, they create hydrogen sulfide gas, which is responsible for the rotten egg smell.

In some cases, the odor could also stem from the water supply itself. If both hot and cold water have the same sulfuric smell, the issue might originate from the source, such as well water with high sulfur content. However, if the odor is only present in hot water, the water heater is the likely cause. For persistent issues, homeowners can rely on our professional tank-based and tankless water heater repair services to diagnose and resolve complex odor problems.

Flushing the Tank to Remove Bacteria

Over time, sediment builds up at the bottom of the tank, creating a breeding ground for bacteria. Draining and cleaning the tank can disrupt that environment and reduce the problem. A professional plumber can flush the system safely, removing stagnant water and built-up sediment that may be contributing to the odor.

Replacing the Anode Rod

Magnesium and aluminum rods are more prone to reacting with bacteria, leading to the formation of hydrogen sulfide. Switching to a zinc or aluminum-zinc alloy anode rod can help reduce the chemical reaction responsible for the odor. Older units with heavy sediment buildup or corroded tanks are more prone to chronic odor issues. So if the odor persists despite replacing the rod, water heater replacement may be the best solution to eliminate the problem entirely.

Adjusting Water Heater Temperature

Since certain bacteria thrive in warm environments, adjusting the water heater’s temperature can help limit their growth. Raising the temperature to about 140° can kill bacteria inside the tank, but this should be done with caution, as higher temperatures increase the risk of scalding. If you’re unsure about adjusting the settings safely, consulting a plumber is the best course of action. For newer units, proper water heater installation also plays a role in preventing future bacterial growth by reducing the chances of sediment buildup.

In some cases, a temporary high-temperature flush—where the water heater is set to a higher temperature for a short period before being lowered again—can help eliminate bacteria without causing long-term risks.

When to Call a Professional

If flushing the tank, changing the anode rod, and adjusting the temperature don’t resolve the issue, further inspection may be needed. A plumber can assess whether the water supply itself is contributing to the odor or if other issues, such as deteriorating pipes or excessive sediment buildup, are making the problem worse.

Ignoring the smell won’t make it go away. Left untreated, bacterial growth inside the tank can accelerate corrosion, shortening the lifespan of the water heater. Persistent odors can also signal deeper water quality concerns that should be addressed before they lead to more extensive plumbing issues. In cases where the current unit is aging or inefficient, tankless water heater replacement offers a long-term solution with improved energy efficiency and fewer maintenance concerns.

Say Goodbye to Smelly Water

Gold Star Plumbing & Drain specializes in diagnosing and fixing water heater problems If your hot water smells off, let’s take care of it before it gets worse.

Contact us today to schedule an appointment.