How to Eliminate Rotten Egg Smell from Water Heaters

How to troubleshoot rotten egg smell in water heaters? What causes the rotten egg odor in hot water, how to diagnose and get rid of the smell? Is it harmful?

What can cause the rotten egg smell?

Hydrogen sulfide gas (H2S) and anaerobic bacteria, combined with the standing hot water inside the tank, are the main reasons for the rotten egg odor in hot water and water heaters.

The bacteria known as "Divibrio Sulfurcans" inside the heater's tank converts the sulfate into the hydrogen sulfide and makes the water smelly. The bacteria is non-toxic (except in extremely high concentration), but it can affect the taste and odor of water.

Except for the water heaters, the sulfur odor can also develop in corroded iron piping, even if the incoming city water is chlorinated. This occurs when water was stored and inactive for several days, the concentration of chlorine is low and level of sulfates high.

It is easy to diagnose the problem by smelling the water coming out of the cold and hot water tap. If the smell is coming from the hot water tap only, the problem is in the water heater.

Rotten egg odor caused by the sulfur bacteria can be found in any tank-type water heater no matter of the manufacturer; AO Smith, Kenmore, GE, Rheem, Bradford White or any other. It is also found in the groundwater, distribution pipeline, and well systems.

What else can happen

Hydrogen sulfide doesn't produce only bad smell but is also related to corrosion of metal components in the heating system and black stains on the plumbing fixtures.

The good thing is that the hydrogen gas does not affect the quality of water, but if it is present in higher concentration in the air it can be dangerous.

The sulfur bacteria growth can also develop slime, which can clog the pipes, while the presence of iron bacteria, could lead to rusty hot water.

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How to reduce or eliminate rotten egg smell in a water heater

  • Either you have a gas - or electric-powered water tank heater, the odds of getting smelly water are high, but as long as the sulfur level in the tank is low, unpleasant odor is under control.
  • Make sure that the anode rod is not extremely depleted. If it is, recommendation is to replace the anode, not only because of the rotten egg odor, but because it can disrupt corrosion protection. Most of the water heaters are equipped with the magnesium rods, but if you replace it with the zinc alloy rod you will significantly reduce the production of hydrogen sulfide gas while still protecting the metal tank effectively.
  • Make sure to avoid long periods of an inactive heater. Bacteria that produce the rotten egg odor likes the warm environment, no water movement and if there is a lack of oxygen. One of the recommendations from the manufacturers and plumbers is to keep the temperature of hot water high enough (160 F), and if done for a few hours it can reduce the level of sulfur bacteria or even eliminate it.
  • Keep in mind that bacteria that causes the rotten egg smell can enter your home plumbing system through the distribution system and well water.
  • Water softeners that are used to treat the hard water and reduce the sediment build-up are increasing the chances of getting the rotten egg smell, as they speed up the process of the anode rod depletion.

How to remove the rotten egg smell from the water heater

One of the easiest ways to eliminate the rotten egg odor from your gas or electric water heater is to flush the tank with the chlorine bleach solution, or if you are looking for a safer option - hydrogen peroxide. Like with the shock-treatment of the pools, shock-chlorination is the simplest way to disinfect and remove the smelly water from your heater. If the tank water is heavily infected than several repetitions should be done. To remove the bacteria totally from the plumbing, tank, faucets, and fittings, chlorination should be done properly or the problem might return back.

Procedure to eliminate the odor using the hydrogen peroxide

  • Turn off the electrical and gas supply to the heater.
  • Close the cold water supply to the heater on the main shut off valve.
  • Drain a few gallons of water from the tank using the drain valve. Close the valve after.
  • Remove the anode rod by unscrewing it from the top of the water heater. Alternatively, you can remove the TPR valve or water inlet/outlet extensions.
  • Use the funnel and pour 3% hydrogen peroxide in a ratio of 1 cup for every 10 gallons. For the 50-gal water heater, use 5 cups of hydrogen peroxide.
  • Put the anode rod back. Keep in mind that if the rod was heavily depleted, the recommendation is to install a new one.
  • Turn the cold water back on and refill the heater.
  • Leave the peroxide mixture inside the tank for several hours.
  • Open all the hot water faucets so the peroxide mixture, while water is running, can clean the pipes.
  • When done, close the hot water taps.
  • You can also open the drain valve to remove the sediments if present.
  • Close the drain valve.
  • Fill the system again and bleed all the air from the heater.
  • Resume the power.


Rotten egg odor is not harmful but is irritating. The Sulphur smell is a common problem in many households, hard to remove but when done correctly could save you lots of money.

If thinking about buying a new water heater, my recommendation is to check Rheem Marathon series as they utilize the plastic tanks, do not use anode rods, so chances of getting the rotten egg smell are minimal, and the warranty is a lifetime. You can also buy a tankless which heats water on demand resulting in fresh hot water delivery. It does not store water and does not utilize the anode, which are the main reasons for the rotten egg problem.

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