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Hot Water Smelling Like Rotten Eggs?

Does the hot water that reaches your home tend to smell like rotten eggs? Well, you are not alone. This is a quite common problem that many homes experience. Before you get all kinds of crazy ideas why this might be the case, there’s a perfectly logical explanation.

Rock and soil formations in ground water contain minerals such as sulfur, which combine with oxygen to form sulfates. These sulfates dissolve and are released into the groundwater.

Bacteria known as anaerobic-bacteria thrive in environments with little oxygen, in wells systems, water distribution systems and water heating systems. These bacteria use sulfur as an energy source and chemically change natural sulfates into hydrogen sulfide. Sulfur reducing bacteria are the main producers of large amounts of hydrogen sulfide.

water smells

Hydrogen sulfide is a gas that has the offensive smell of rotten eggs, and is the cause of the taste and smell of rotten eggs in water from well systems, water distribution systems and water heating systems. It is not harmful in its dissolved state as only small quantities are present. However, the gas can be lethal to humans and animals if exposure reaches large amounts.

Hydrogen sulfide gas is produced in a number of different ways. It’s produced naturally in groundwater or by sulfur and bacteria in wells as explained earlier or, it can occur due to chemical reactions in water distribution systems and water heaters. Pollution from landfills, sewage systems, pipelines, chemical labs and many other sources can also produce hydrogen sulfide gas.

In heating systems like water heaters, magnesium and aluminum anodes in the heaters, react with anaerobic bacteria to produce hydrogen sulfide gas hence the rotten eggs smell sometimes present in hot water. The smell will be more noticeable in hot water because the gas tends to rise in hot water. Let us look at how this reaction occurs.



Water heaters are ideal for the conversion of sulfates to hydrogen sulfate gas. They have a warm environment where bacteria can live, and anodes rods made of magnesium or aluminum meant to reduce corrosion within the water heater tank. These anodes rods have electrons that help in changing sulfates to hydrogen sulfides. The anodes are usually 1/2 to 3/4 inches in diameter and 30 to 40 inches long within the heater tank.

The smell of hydrogen sulfide gas in water is also present at low temperatures and you can find out the cause by smelling the water coming from both hot cold/water taps. You can identify the factors that can contribute to the smell of hydrogen sulfide gas in hot water using one of the following methods listed below.

  • If the smell is from the hot water tap, then the problem could most likely be from the water heater.
  • If the smell is from both the hot and cold water taps, from water treated with water softener and not from untreated water, then the problem is likely to be caused by the sulfur bacteria in the water softener.
  • If the smell is strong in both taps once you open them then decreases or goes away as the water runs, or if the smell varies from time to time, then the problem could be caused by the sulfur bacteria in the well or water distribution system.
  • If the smell is strong in both cold and hot taps and is constant throughout, chances are the problem is most likely caused by hydrogen sulfide in the groundwater.


What Should You Do?

There are a few things you can do to stop the production of hydrogen sulfide gas in your water heater. If you are not familiar with the workings and maintenance of the water heater, contact a professional to do the following.

  1. Replace the Magnesium Anode with Aluminum/Zinc Anode

Most water heaters have a magnesium or aluminum anode attached to a plug on top of the heater. You can remove it by turning off the water, releasing the pressure in the water heater and unscrewing the plug.

Replace the magnesium or aluminum anode with an anode made of aluminum/zinc alloy and reattach the plug.

Removing the anode can reduce the life of the water heater. It is advisable to consult a water heater dealer to find out whether a replacement anode made of aluminum/zinc can be installed in your heater. A replacement aluminum/zinc anode can help protect the heater from corrosion without producing hydrogen sulfide gas.

  1. Disinfect and Flash Water Heater with Hydrogen Peroxide or Chlorine Bleach Solution

Flashing the water heater with hydrogen peroxide or chlorine will kill the sulfur bacteria. If some sulfur bacteria survive after flashing or you allow the water heater to stay a long time without being used, the problem will return within a short time. Hydrogen peroxide is considered safer to use than chlorine bleach solution.

  1. Increase the Water Heater Temperature

Increasing the temperature of the water heater to 160 degrees Fahrenheit (71 degrees Celsius) will kill the sulfur bacteria. Flashing the water heater afterwards will help remove the dead bacteria and smell.

Note: Increasing the temperature of the water heater can be dangerous and you will need to consult the manufacturer or dealer on whether the relief valve is functioning and any other recommendations or safety guidelines that you should enforce. You should also lower the thermostat settings to make sure the water temperature is reduced following the procedure so as to avoid scalding from hot water and high energy costs.

  1. Install a Powered Anode Rod

If installing an aluminum/zinc anode does not solve the problem, then you should install a powered anode rod. These rods do not have magnesium or aluminum for bacteria to react with, so they do not need replacement and there will be no smell.

Powered anode rods are much more expensive than the other standard rods. Make sure you consult a professional so that they install the right anode head for your water heater as installing the wrong head will not solve the problem and could cause a short circuit.


What Not to Do

Replacing magnesium or aluminum anode with an aluminum/zinc anode is the cheapest way to fix the hydrogen sulfide gas problem in your water heater. Zinc is the key ingredient since aluminum alone will not eliminate the problem. You should never attempt to do the following:

  • You should never put two anodes in your tank as even two aluminum/zinc anodes may make the smell worse.
  • Do not soften the water in the tank as softening will increase water conductivity, speed up bacteria anode reaction and increase the hydrogen sulfide gas produced.
  • Refrain from installing any parts or do any maintenance and repairs if you are not familiar with the workings of the water heater. Seek help from a professional to avoid damaging your water heating system inadvertently.


The above tips should be enough to help you get rid of the smell of rotten eggs in your water. Consult an expert in water heaters and water distribution systems if you’re still unable to solve the problem.

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  1. Even if you are aware of how to replace an anode, I think it’s still best to just consult with a professional. It’s just a precaution that might help ensure that there won’t be problems later on. It’s also just reassuring to have a professional opinion.

  2. It’s interesting that a new powered anode rod could help reduce the smell of sulfur in the hot water. It makes sense that it could be beneficial as it wouldn’t need to be replaced. I’ll definitely have to call a professional to see if it’d be possible to get one installed or if I should just replace the system. Thanks for sharing!

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