Why Hot Water has Rotten Egg Smell

why water heater smells like rotten eggs

Not everyone experiences it, but for those who do, did you ever wonder why water heater smells like rotten eggs? For the sake of simplification, let us assume that the source of the rotten smell is really your water heater. What does it smell so bad and what do you do?

The Cause

If you have a case of smelly water, this can be attributed to the presence of anaerobic bacteria. It reacts with the sulfur, magnesium, and aluminum materials that make up the sacrificial anodes that are part of the water heating system.

When the bacteria comes in contact with the materials, it produces hydrogen sulfide, which has a similar smell to rotten egg. This type of problem is usually observed in areas where the supply comes from well systems. The installation of a water softening system may make the smelly problem become worse.

Starting Solution

A quick fix solution to the rotten egg smell is to turn off the cold water valve feeding the water heater and open the closest hot water faucet. This is done to relieve pressure so that you can drain some water from the tank. You need to open a side of the plumbing so that you can put in one pint of drugstore-type hydrogen peroxide for every 20 gallons of water.

Close up everything before turning the cold water back on. Allow the water to run from all faucets for a while until you notice the odor is gone. The problem is that once the water heater goes unused you need to repeat this process.

When the smelly water is isolated to a sink, pour chlorine bleach down the drain and basin overflow. This should take care of the bacteria causing the smell. It is essential to know that in some places the cause of the smell is the sulfur in the water. This means that the sulfur has to be neutralized to remove the rotten egg smell.

Better Solution

To get a considerably long term solution to the rotten egg smell, one of the suggested alternatives is to use aluminum/zinc alloy as a replacement for the standard aluminum or magnesium anode rod. Why is this successful?

The zinc in the alloy balances the reeking smell produced by aluminum anodes. This is likewise considered by many as the cheapest permanent solution possible for solving the rotten egg smell. Using two anodes (an aluminum and a zinc one) may only worsen the odor. Stick to the alloy type.

When using the alloy variants, there are four types that you can choose from. You have the solid hex- head, flexible hex-head, solid combo, and the flexible combo. These are important in choosing the right type of anode. The hex-heads have their own port located at the top of the water heater. Combo anodes on the other hand share the port for the hot water outlet. Unscrewing the nipple will reveal the anode.

What to Avoid

When attempting to get rid of that rotten egg smell coming from your water heater, make sure that you do not remove the standard sacrificial anode without replacing it. Removing the standard anode is the right solution, but, if you do not replace it, you will fast-track the formation of rust and corrosion.

Replacing the magnesium anode with an aluminum one also does not solve the problem. Why? Because aluminum will create the same type of rotten egg smell as magnesium; it’s all about the chemical reaction. So make sure that when you remove the anode, you replace it with the proper one. Otherwise, you will be voiding the warranty of the manufacturer and shortening the life of your water heating system.

Now that you know why water heater smells like rotten eggs, you can choose what option to use. Consult a licensed plumbing professional to know more about your options.


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