What Causes That Rotten Egg Smell in Your Water Heater?

If you’ve noticed a sulfur or rotten egg odor coming from your hot water, you’re not alone. This common problem usually originates in your water heater tank and is often caused by anaerobic bacteria reacting with the sacrificial anode rod inside the heater. These bacteria are typically harmless to your health, but they can produce hydrogen sulfide gas, which smells like rotten eggs and is particularly strong when hot water is used in the shower, sink, or dishwasher. Homes using well water are more prone to this issue, but it can also occur in municipal water supplies under certain conditions. The anode rod—typically made of magnesium or aluminum—is designed to prevent corrosion inside the tank, but unfortunately, it’s also what the bacteria feed on to produce that foul smell.

Effective Solutions to Eliminate the Sulfur Smell

Fixing a smelly water heater depends on the severity of the issue. The most straightforward solution is flushing the tank and disinfecting it with hydrogen peroxide or a chlorine bleach solution. This kills the bacteria responsible for the hydrogen sulfide gas. In some cases, replacing the magnesium anode rod with a zinc or aluminum-zinc alloy rod can reduce or eliminate the smell altogether, since zinc doesn’t interact with bacteria in the same way. For persistent problems—especially with well water—it may be necessary to install a whole-house water filtration system or a point-of-entry chlorination system to treat the water before it enters the water heater. If the tank is very old or corroded, replacing the entire unit may be the most cost-effective long-term solution. A licensed plumber can help you determine the best course of action.

Prevention Tips and When to Call a Professional

Once you’ve resolved the smell, it’s crucial to take steps to prevent it from returning. Start with annual water heater maintenance, including flushing the tank and inspecting the anode rod. If you’re on a well system, have your water tested regularly for sulfur and iron bacteria levels. Installing a powered anode rod can also help—it doesn’t corrode over time and doesn’t support bacterial growth. If you’re still noticing the smell after cleaning and replacing the rod, or if your water shows signs of discoloration or metallic taste, it’s time to call in a professional plumber. Persistent sulfur odors could indicate deeper issues like contaminated water sources, tank corrosion, or ineffective filtration systems. Staying ahead of the issue not only protects your plumbing system but also improves the quality of your home’s water and your peace of mind.