Why your water heater has a bad smell: Possible causes and how to get rid of it

If your hot water smells bad, 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.

If you need any replacement parts for your appliances, you can enter your model number at AppliancePartsPros.com to order them. Most orders arrive in just two business days, and we have thousands of free guides to show you how to install your new parts.

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.

What causes the bad smell in my water heater?

When your water heater smells bad, like sulfur or rotten eggs, it’s typically a sign that hydrogen sulfide gas has built up. This gas is produced when sulfates in your water react with certain components inside the heater, like the anode rod. Here are the most common causes for this problem:

Bacterial growth inside the water heater

The warm, moist environment inside a water heater can sometimes encourage bacterial growth, especially if water remains stagnant for long periods. These sulfur-reducing bacteria feed on sulfates in the water and release hydrogen sulfide gas, which causes the 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.

This issue is more prevalent in homes with well water, as it tends to contain more sulfate.

Anode rod reaction

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.

Troubleshooting steps

Step 1: Check your cold water

Determine whether the sulfur smell is present in both your cold and hot water. Run the cold water tap to see if the odor is noticeable. If the smell is only present in hot water, the issue is likely in the water heater. If both cold and hot water smell like sulfur, the problem may stem from your water supply.

Step 2: Flush the water heater

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 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.

Step 4: 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 5: Install a water filtration system

If the smell is coming from your water supply, a whole-house water filtration system may be needed to remove sulfur from the water before it enters the water heater. This will help eliminate the sulfur odor in hot water for good.

People also ask

Why does my water heater have a bad smell?

The most common reason a water heater has a bad smell is due to the production of hydrogen sulfide gas, which creates a sulfuric or rotten egg odor. This can be caused by bacterial growth inside the water heater or a reaction between the anode rod and sulfates in the water. The smell is usually more noticeable in hot water because the heat intensifies the sulfur odor.

How do I get rid of the bad smell in my water heater?

You can get rid of the smell by:

• Flushing the water heater to remove sediment buildup.
• Replacing the anode rod with a zinc or aluminum one to prevent further reactions.
• Sanitizing the tank using hydrogen peroxide to kill bacteria.
• Increasing the water heater temperature temporarily to kill the bacteria. Regular maintenance and cleaning will help keep the smell from coming back.

Why does only my hot water smell bad and not the cold water?

If only your hot water smells bad, it’s likely an issue with your water heater. The anode rod in the heater can react with the sulfates in the water to produce hydrogen sulfide gas, which causes the sulfur-like odor. Cold water doesn’t pass through the heater, so the smell is usually absent in cold water.

Is the bad smell from my water heater harmful?

While the bad smell itself is unpleasant, it’s not generally harmful to your health. However, the presence of hydrogen sulfide gas can corrode plumbing and water heater components over time, leading to costly repairs. It’s important to address the issue promptly to avoid damage to your water heater and plumbing system.

Can I fix the bad smell in my water heater myself?

Yes, you can often fix the bad smell in your water heater yourself by following these steps:

1. Flush the water heater tank to remove any bacterial growth or sediment.
2. Replace the anode rod with a zinc-aluminum or powered version to prevent the reaction that produces hydrogen sulfide gas.
3. If the smell persists, add hydrogen peroxide to disinfect the tank or install a water filtration system if sulfur levels in the water are high.

Additional information

Thanks for reading! If you still need some replacement parts, grab your model number and head over to AppliancePartsPros.com. We offer over two million parts and most orders arrive in two business days. If you need some help with finding the right part or placing an order, you can contact our team at 1 (877) 477-7278.

While you’re waiting for your new part to arrive, you can explore our DIY blog and watch thousands of video tutorials on our YouTube channel.Be sure to follow us on Facebook, Twitter and Instagram to see our latest repair guides!