water smells like rotten eggs

You may have heard of the amazing hot springs within Yellowstone National Park in Wyoming — and if you’ve ever visited the Mud Volcano and Sulfur cauldron, you won’t likely forget the pungent odor of…rotten eggs.

While that’s an extreme situation, there’s a similar reason why your home’s water can sometimes smell (and taste) like rotten eggs.

What causes the smell?

That particular odor is usually caused by hydrogen sulfide gas in the water. At home, this happens when certain bacteria in water react with sulfur and the magnesium and aluminum anodes that come in most water heaters. It also occurs naturally in some groundwater where decomposing organic matter is released into water through underground springs.

Sometimes the odor is noticeable only when the water is turned on. And because heat forces the gas into the air, it seems stronger when running heated water (such as in the shower). In fact, if you only smell it when using your hot water, it may be the reaction occurring inside your hot water heater, and not a problem with the water supply.

Is it harmful?

Generally, the odor and taste are so unpleasant at very low levels that most people would not ingest enough for it to be harmful, although an OSHA document warns that you can quickly become desensitized to it, and it has harmful effects when inhaled as a gas, even at low levels.

It is primarily a nuisance as a water contaminant, although it is corrosive to certain metals, corroding pipes, discoloring copper or brass fixtures, and causing black stains on silverware. It can also affect the taste and appearance of coffee, tea, and foods cooked in the water.

There are many minerals and chemicals found in the drinking water across the country, but the rotten egg odor is specific to hydrogen sulfide gas. Although it is usually safe to drink, it can mean there is a water contamination issue that you should address.

How do you deal with it?

Locating the source is a good way to start dealing with this problem.

If the smell is only from hot water:

If it happens only when you’re running hot water, then the problem is probably in the water heater. You may be able to solve the problem by switching the standard magnesium or aluminum anode rod with an aluminum/zinc alloy rod. Contact a professional plumber for a proper inspection.

If the smell is in both the hot and cold water:

If it’s in water treated by a water softener but not in the un-softened water, the problem is likely to be sulfur bacteria in the water softener. Hopefully, a change in the water softener solution will resolve the problem.

If the smell is in both the hot and cold faucets when first turned on:

In this case, the problem is likely in the groundwater. If however, the smell diminishes or goes away after the water has run for a bit, it’s likely that there’s sulfur bacteria in the well or distribution system. In either case, this could be a sign that there is a more dangerous problem in your water supply.

You can purchase test kits that will check the levels of hydrogen sulfide as well as sulfate, sulfur bacteria, and iron bacteria in your water. If there’s any doubt, or you want more information, it’s best to call a local plumbing professional.