If your hot water smells like rotten eggs, don’t panic. It’s almost certainly something you can fix on your own, and there are a few different ways you can try to fix it.

First, to make sure your hot water heater is the source (and that this is the blog post you’re looking for), check your cold water. If it doesn’t smell like sulphur (that classic rotton egg smell), then you’re in luck — it’s almost certain that you can fix the problem at your water heater. But if your cold water does smell, you should start your web search again, because this article only addresses how to fix rotten egg smells in your hot water.

Next, make sure it’s actually the water that’s causing the odor. If your shower, tub, sink, or floor drain dries out completely, you’ll have a completely open pipe between your septic or sewer line and that drain — and it won’t smell pretty. Just run the water for 10 seconds to re-fill the drain, and maybe even pour in a little bit of chlorine bleach to help kill odor-causing bacteria near the top of your drain.

But if you’ve confirmed that the source of the smell is your hot water, read on for some fixes.

Why does my hot water smell like rotten eggs?

Depending on your water source, your water will contain various amounts naturally occurring sulfur. Your water probably also contains naturally occurring sulfate-reducing bacteria. These organisms are harmless to humans, and if you’re on city-treated water, most are killed (along with any harmful bacteria) when your city adds chlorine to the water. But if you’re using well water (which isn’t chorlinated), more of those naturally occurring organisms are in your water, and your water might also contain higher concentrations of sulfur.

If you check the section of Wikipedia’s article on sulfate-reducing bacteria titled “Problems caused by sulfate-reducing bacteria,” it says:

sulfate-reducing bacteria can create problems when metal structures are exposed to sulfate-containing water: Interaction of water and metal creates a layer of molecular hydrogen on the metal surface; sulfate-reducing bacteria then oxidize the hydrogen while creating hydrogen sulfide, which contributes to corrosion.

In other words, if you take sulpher, plus this bacteria, plus a corrosive metal inside your water heater, the end result is that the metal will corrode and the bacteria will create hydrogen sulfide (H2S) … which smells like rotten eggs:

Hydrogen sulfide gas smells like rotten eggs

If you’ve read my previous post on anode rods, you’ll recognize right away the source of your stinky water: the metal anode rod in your water heater. Your anode is most likely made of magnesium or aluminum, and it’s designed to corrode (so that your tank won’t). But when the bacteria eats away at your anode, one of the byproducts is stinky H2S gas. But read on to find out why you shouldn’t just yank that anode rod from your tank.

Things that can make the problem worse

If you use a water softener, the water softening process increases the conductivity of the water in your tank, which corrodes your anode even faster, which lets the bacteria form smelly gas more quickly. So if you have well water (which is probably hard, untreated, and has more sulfur and bacteria) and you soften it, you’re far more likely to have smelly water.

Your problem gets even worse if water doesn’t flow though your tank often, like at a cabin or vacation home. Water heaters that sit unused for weeks or months allow the H2S gas to really build up — which is actually why I started looking into how to solve this problem. Our cabin gets its water from a community well (strike one), we use a water softener (strike two), and the water in our tanks sits for weeks at a time (strike three). If it’s been a while since we’ve visited, you’ll hop out of that first shower smelling even worse than when you got in.

How can I get rid of the smell?

Depending on how bad the problem is, and how many “strikes” you’ve got against you, there are a few different things you can try to fix the smell. They all focus on either preventing the formation of the H2S gas, or killing the bacteria that’s causing it. Some plumbing “experts” might tell you to just remove the anode from your water heater. I won’t lie — that will fix the issue… but it’s a dumb idea. Removing your anode actually voids your water heater’s warranty. Why? Because removing the anode will cause premature rust and leaking! Just don’t do it.

Fight H2S with H2O2

One way to fix the problem pretty quickly is to shut off your water heater’s cold water inlet valve, drain some of the water from your water heater (or even do a full or partial flush), then disconnect the metal hose that connects to the cold water side of your water heater, like this:

Opening the cold water inlet on your water heater

Using regular old 3% hydrogen peroxide (H2O2) solution that you can get at any drug store (a 32 oz bottle should be less than $1), pour in one cup (8 oz) of hydrogen peroxide for every 10 gallons of your water heater’s size. For example, if you have a standard 40 gallon tank, you’d pour in 4 cups (or the whole 32 oz bottle).

Pour in 1 cup of hydrogen peroxide for every 10 gallons of tank capacity

Re-connect the hose, turn the cold water valve back on to refill your tank, then let it sit for a couple of hours. The hydrogen peroxide will kill the bacteria — and the smell along with it. You could technically also use chlorine bleach, but the hydrogen peroxide is much safer. Hydrogen peroxide is good at killing bacteria, but it’s also generally recognized as environmentally safe by the FDA, because it degrades to form oxygen and water. If it’s been a while since we’ve been to our cabin, this is one of the first things I do when we arrive.

Replace your anode with an aluminum/zinc one

Another way to possibly fix the rotten egg smell in your water heater is to remove the magnesium or aluminum anode from your water heater and replace it with one that’s made of both zinc and aluminum, like this one (make sure you get one that’s the same style and size as your current anode). If you don’t use a water softener, this will probably do the trick. If you do use a water softener, then this might do the trick… but it’s possible that your softened water is so conductive that even a zinc-aluminum anode doesn’t work.

If the zinc-aluminum anode does work, you may want to consider trying a powered anode, because you’ll never have to replace it. But if the zinc-aluminum anode doesn’t work, don’t waste your money on a powered one, because it won’t work either. You may just have to treat your water with hydrogen peroxide from time to time.

If Neither Solution Works

If neither of the above solutions fix your problem, then it’s possible that the stinky water exists “upstream” of your water heater, and you might want to experiment with some water filtration solutions to remove the sulfur. If that’s the case, your cold water probably smells too, but maybe you don’t smell it as much because it’s not being propelled by the steam from your hot water.

Hopefully, one of the “easy” solutions works for you, and you can avoid rotten egg smelling water from now on!

As always, I welcome your comments, feedback, and questions below!