Why your water heater smells like rotten eggs and how to fix it

If your hot water smells like rotten eggs every time you turn on the tap, it’s not only unpleasant but also a sign that something’s off with your water heater. Don’t worry, though, it’s fixable. We’ll break down why your water heater is causing that nasty odor and, more importantly, how you can get rid of it for good.

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Important: The information provided in this article may not apply to your specific appliance model. While we strive to offer helpful advice for DIY appliance repairs, variations in models and configurations can lead to differences in troubleshooting steps, error codes and part replacements. For the most accurate guidance, we strongly recommend consulting the technical sheet for your specific appliance model.

Why does my water heater smell like rotten eggs?

The main culprit is typically hydrogen sulfide gas. This gas, which has a distinct sulfuric or rotten egg odor, is produced by the interaction between your water heater and the water itself. This issue is more common in homes with well water, as it typically has higher sulfate content.

Here’s a breakdown of the most common reasons:

Bacterial growth in the tank

Over time, bacteria can grow in the warm, moist environment of the water heater tank, especially when it hasn’t been used for a while. These bacteria feed on the naturally occurring sulfates in the water, producing hydrogen sulfide gas as a byproduct, leading to that rotten egg smell. Keeping the water heater set to at least 140°F (60°C) will make it harder for bacteria to grow. However, be mindful of the risk of scalding at higher temperatures.

Reaction with the anode rod

Most water heaters contain an anode rod made of either magnesium or aluminum. While the anode rod is essential for preventing corrosion inside the tank, it can also react with the sulfates in your water. This chemical reaction creates hydrogen sulfide gas, which can cause the smell.

This issue is particularly common in homes that have well water or high sulfate levels in the water supply. If your water heater’s anode rod is causing the odor, you’ll notice that the smell is more pronounced when you run hot water.

Sulfur in your water supply

In some cases, the sulfur smell isn’t directly related to the water heater but is due to high sulfur levels in your water supply. This can affect both hot and cold water, but the heat intensifies the odor, making it more noticeable in hot water. If this is the case, you may need to consider a water filtration system to remove excess sulfur from your water.

Read more: Water heater not hot enough? Here’s how to fix it

Troubleshooting steps

Step 1: Flush the water heater tank

1. Turn off the water heater and let it cool down. For gas heaters, set the gas control valve to the “pilot” position.
2. Locate the drain valve on the tank. It is typically located near the bottom and looks like a hose bib with a threaded end.
3. Attach a garden hose to the valve and run it to a drain, utility sink, or outside.
4. Open a hot water faucet in your home to allow air into the system and help with drainage.
5. Open the valve and allow the tank to drain completely. Be cautious as the water can be hot.
6. To further flush the tank, turn the cold water supply back on for a few minutes while the drain valve is still open. This helps to flush out any remaining sediment that may be settled at the bottom of the tank.
7. Once the water runs clear and you have flushed the tank adequately, close the drain valve by turning it clockwise.
8. Disconnect the hose from the drain valve.
9. Turn on the water supply to refill the tank. Keep the hot water faucet open to release any air trapped in the system.
10. For electric heaters, switch the power back on at the breaker box. For gas heaters, set the gas control valve back to the desired temperature.

Step 2: Replace the anode rod

1. If you have an electric water heater, switch off the breaker at your electrical panel. For gas water heaters, turn the gas valve to the “off” position.
2. The anode rod is typically located on the top of your water heater and can be accessed by removing the hexagonal head cap or by unscrewing it from the top of the tank.
3. To prevent any water spills, attach a garden hose to the drain valve at the bottom of the tank and drain a few gallons of water.
4. Use a wrench to remove the old anode rod from the water heater tank. Be cautious as the rod may be corroded and require some force to loosen.
5. Carefully insert the new anode rod into the opening at the top of the water heater tank. Use a suitable replacement anode rod. Consider using a zinc-aluminum alloy or powered anode rod, which is known for its effectiveness in reducing odor-causing bacteria.
6. Use a wrench to tighten the rod securely into place to prevent leaks.
7. Close the drain valve and allow the tank to refill with water. Check for any leaks around the anode rod area.
8. Once the tank is filled, turn on the power or gas supply to the water heater.

Step 3: Disinfect the tank

1. Turn off the water heater and drain the tank as described earlier.
2. Turn off the cold water supply valve to prevent more water from flowing into the tank while you drain it.
3. Attach a garden hose to the water heater’s drain valve (located at the bottom of the tank). Place the other end of the hose in a nearby drain, bucket, or outside. Open the drain valve and allow the tank to empty. Be careful, as the water inside can be very hot.
4. Once the tank is empty, close the drain valve. Pour about 1-2 pints of 3% hydrogen peroxide into the tank through the anode rod port or cold water inlet.
5. This amount should be enough to sanitize a typical 40-gallon tank. For larger tanks, you may need to increase the amount of peroxide.
6. Open the cold water supply valve and let the tank fill back up with water. The hydrogen peroxide will mix with the water inside the tank, allowing it to clean the interior surfaces.
7. Allow the water and hydrogen peroxide mixture to sit in the tank for 2-4 hours. This gives the peroxide enough time to kill off any bacteria causing the rotten egg smell.
8. Drain the tank again to flush out the hydrogen peroxide and any remaining bacteria. Refill the tank with fresh water and repeat the flushing process until the water runs clear and odor-free.
9. Once the tank is thoroughly flushed, close the drain valve and let the tank fill up with water again. Turn the power or gas back on and let the water heater resume normal operation.

Read more: How to clean a water heater thermocouple to keep your unit running smoothly

People also ask

Is the rotten egg smell in my water dangerous?

The smell itself isn’t harmful, but it indicates hydrogen sulfide gas, which can be toxic at high levels (though the concentration in your water is typically very low). However, it’s important to address the issue, as it may indicate bacterial growth in the water heater, which can affect water quality.

Why does only my hot water smell like rotten eggs?

The rotten egg smell is usually confined to the hot water because the reaction causing hydrogen sulfide gas occurs in the water heater’s tank, where hot water is stored. The heat accelerates the bacteria’s activity, leading to a stronger odor when you run hot water.

Why does my hot water smell like rotten eggs but not my cold water?

The cold water doesn’t typically smell because it doesn’t go through the water heater, where the bacteria-sulfur reaction happens. The heat in the water heater encourages the reaction between the anode rod and sulfur in the water, producing hydrogen sulfide gas, which causes the odor only in the hot water.

Will a home filtration system get rid of the smell?

Yes, a home filtration system can help get rid of the rotten egg smell in your water by removing hydrogen sulfide (the gas responsible for the odor) and other impurities from the water supply. If the sulfur levels in your water supply are high, installing a whole-house filtration system can make sure that all the water is free from the odor.

Read more: How to clean a water heater thermocouple to keep your unit running smoothly

Additional information

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