Why do my toilet & washing machine smell like rotten eggs after a lot of rain?

Updated February 21, 2017

When your washing machine or toilet smells like a rotten egg after a rainstorm, you need to know the cause of the smell so you know the risks that come along with it. Sulphur smells like rotten eggs, and sulphur deposits may find their way into your house's water supply.

Sulphates in Water Supply

Sulphates enter your house's water supply when the rain water picks up sulphate deposits in the ground. Sulphate deposits occur naturally from decaying plants or sulphate mineral deposits in rocks. The sulphate travels with the water through the ground and into wells or other water supply resources where the sulphate-contaminated water flows into your house's water supply.


Bacteria that breaks down sulphate deposits into hydrogen sulphide may live in your house's water supply system. The bacteria likes to grow in areas with little oxygen, such as hot water heaters, the bottom of water wells and water softeners. The bacteria will also produce a black slime that will stain the clothes in your washing machine.

Heat and Use

You use your toilets constantly, and each time you use the toilet it refills the toilet's tank with fresh water. The toilet may be one of the first plumbing fixtures in the house to have the sulphate-tainted water introduced. Your washing machine, on the other hand, will use heated water on certain settings. The presence of heat and steam will release the rotten egg smell in tainted water more than cold water, making the smell even more intense in the washing machine.


In high levels, hydrogen sulphide can be fatal and combusts easily. Normally the amount of hydrogen sulphide in a house's water supply is not enough to be fatal. Those who consume the tainted water may experience diarrhoea and dehydration since hydrogen sulphide is a laxative. Other symptoms of exposure may include nausea and dizziness in more extreme cases. The black slime produced by the bacteria will clog pipes and promote pipe corrosion. The hydrogen sulphide will also reduce the cleaning power of some bleach-based clothes detergents. Only a professional water analysis will let you know the concentration levels in your house's water, which will determine the level of risk.

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