Why does my washing machine smell like eggs?

Updated February 21, 2017

When you smell an offensive odour similar to eggs in your washing machine, your house's water supply possibly contains sulphates. The presence of sulphates and bacteria that breaks down sulphates can pose several problems for your plumbing and health as well as the cleaning effectiveness of your washing machine.

Sulphates in Groundwater

Most groundwater contains at least some levels of sulphates, although the concentration is so low that you do not notice. When water runs through the soil during precipitation, the water will contact plant decay or minerals containing sulphates. These sulphates are transported by the water into the water well or other water supply source, where it is then introduced into your house's water supply.


Bacteria that live in your house's water supply system will break down sulphates in the water to produce hydrogen sulphide gas. The gas will give off a rotten egg smell. The bacteria live in parts of the water supply system that get little oxygen, such as hot water heaters and water softeners. The bacteria also will typically live in the hot water side of the supply system, although the bacteria may also be present in the cold water side. Smelling the cold water running out of your faucet will help you tell if the bacteria are also present in the cold water supply or if they are isolated to the hot water supply.

Plumbing Problems

Sulphates in your house's plumbing may lead to problems with your house's plumbing since the sulphates will leave deposits in your pipes that can lead to clogs. The bacteria in your plumbing system will produce a black slime that will also clog pipes, corrode pipe walls and stain the clothes in your washing machine. The higher sulphate levels in your washing machine's water will negate some of the cleaning effectiveness of chlorine bleach detergents.


Contact a professional to test your water supply for the presence of sulphates before you attempt to treat the problem. Replacing the magnesium anode in the hot water tank may help eliminate the problem if it is isolated to the hot water supply, as will cleaning the hot water heater with bleach and draining out all of the water. If sulphate is present in your house's entire water supply system, you will need to install a whole house water treatment system that will remove the sulphates from the water supply.

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