Question: How can I get rid of the rotten egg smell of the water at our cottage? It affects both the hot and cold supply. I’m told dumping chlorine down the well may help, at least for a while. What are my options?
Why Well Water Smells Like Rotten Eggs
If both your hot and cold water smell, you’re almost certainly dealing with sulphur water — more specifically, hydrogen sulfide gas dissolved in the water. That distinctive odor comes from sulphur compounds in solution, and that detail matters because once something is dissolved, ordinary filtration won’t remove it.
You can install sediment filters, cartridge filters, or even a water softener, but none of these will eliminate dissolved sulphur compounds on their own. This isn’t a filtering problem. It’s a chemistry problem, and it needs to be approached that way.
The Sulphur Water Fix That Actually Works
Over the years I’ve seen one solution work consistently in every situation where it has been applied. It involves installing a small metering pump that injects 35% hydrogen peroxide into the water line at roughly 25 parts per million (ppm).
This approach doesn’t mask the smell. It changes the chemistry of the water. Hydrogen peroxide oxidizes the sulphur compounds, breaking them down so they can no longer produce odor. Once oxidized, the treated water is typically passed through a carbon filter or water softener before moving on to taps and fixtures. I have never seen the combination of hydrogen peroxide injection followed by carbon filtration fail to remove rotten egg odours, even in extreme cases.
An Extreme Example of Sulphur Water
A farmer friend of mine, Scott, drilled a new well in an area where sulphur water is common. When the driller hit water, Scott was 100 yards away, downwind, walking back from the barn. Even at that distance, outdoors, the smell was unmistakable and overpowering.
In his case, hydrogen peroxide injection followed by installation of a water softener downstream from the injection pump solved the problem completely and permanently. Disinfecting the well would have done nothing because the sulphur was already present in the groundwater itself.
Two Different Types of Sulphur Water
In my experience, sulphur water behaves in two distinct ways.
In some wells, the water initially smells fine, but over time the sulphur odor develops and persists. These cases often involve water rich in iron and non-odorous sulphur compounds. When certain microbes enter the well and begin feeding on those compounds, they produce hydrogen sulfide as a byproduct, creating the familiar rotten egg smell.
If this is your situation, disinfecting the well can offer relief and sometimes long-term improvement, though rarely permanent. Dumping hydrogen peroxide down the well will disinfect it, much like bleach does.
The second type of sulphur water smells like rotten eggs immediately, right from the start. That was Scott’s situation. In cases like this, disinfecting the well won’t help because the sulphur compounds are already present in the groundwater before it enters the well. This isn’t a contamination issue; it’s a matter of water chemistry. The only dependable solution is a system that chemically changes the sulphur compounds as the water enters the house. Hydrogen peroxide injection followed by filtration works beautifully for this and eliminates all causes of sulphur water, regardless of the source.
Why Filtration Alone Won’t Work
Sulphur compounds are dissolved in the water. Standard filtration cannot remove dissolved substances. Without oxidation first, filters will not eliminate the smell. That’s why hydrogen peroxide injection — or another oxidizing system — must come before filtration in any effective sulphur water treatment setup.
What About Chlorine?
Some systems use chlorine to remove sulphur smell, and chlorine will work chemically, but I don’t recommend it. It is more costly, more troublesome to maintain, and in my view less healthy.
Despite its widespread use in municipal systems, chlorine treatment is associated with byproducts such as trihalomethanes. In North America, exposure to these compounds often occurs not primarily from drinking the water, but from inhaling steam during showers, where the compounds enter the lungs and bloodstream quickly. Many parts of Europe have banned chlorine as a routine disinfectant for precisely these reasons. Hydrogen peroxide, by contrast, breaks down into oxygen and water without creating these byproducts.
Our 20+-Year Experience With Hydrogen Peroxide
We’ve had a hydrogen peroxide injection system combined with a whole-house carbon filter at our place for more than 20 years. It works flawlessly and costs roughly $200 per year for peroxide.
I didn’t originally install it to correct a sulphur problem, but rather as a safeguard to ensure our household water is sterile and pure. Even in homes without odor issues, hydrogen peroxide injection is an excellent way to disinfect water safely. In homes with sulphur smell, it is the most dependable solution I’ve seen.
Final Thoughts on Fixing Sulphur Water
If your water smells like rotten eggs, filtration alone won’t solve the problem. What you need is oxidation first, followed by filtration. In my experience, hydrogen peroxide injection is the simplest, most effective, and most reliable sulphur water fix available.
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