Hydrogen sulfide gas smells like rotten eggs

How to Fix Rotten Egg Smell in your Water 26

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 sulfer, 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 rotton eggs:

Hydrogen sulfide gas 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

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

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!







  • Maggie Dokic

    Hi Steve. Thanks for this post. I’m dealing with this issue now. Interestingly enough, after replacing my old water heater. It didn’t happen before. I already found information elsewhere explaining why that may have been. Anyway, I have a question about the powered anodes. Your suggestion is that if the zinc-aluminum doesn’t work, not to try the powered one, because it won’t work either. I found differing advice on a site dedicated solely to this problem. Can you please expand more on that? I have a water softener and their site is suggesting I get the powered anode in that case. I’m perfectly fine spending the extra cash, as long as it’s going to solve the problem. The smell is so bad the entire house stinks when the hot water is running. It smells SO bad that my daughter was the one who pointed me to your page so I can take care of the problem. Ugh.

    • Hi, Maggie. First, you have a smart daughter. 🙂 Second, you probably didn’t have the problem on your old water heater because your anode rod was likely completely consumed. I’d try a zinc-aluminum anode in your system first. If that works, then go head and spring for the powered one.

      • Maggie Dokic

        Steve, I can’t believe I never came back to thank you for your response. Thank you! I have this link saved and somehow life gets in the way and I still haven’t resolved the issue. I am going to go ahead and try the peroxide today. I do not want to mess with the anode rod yet as I am still fighting with Sears about the fact that they haven’t pulled the permit. (only 13 months after installation…no rush there) I don’t want to do anything to the tank that might prevent me from passing inspection. Once that inspection and permit are done I will be looking into installing the anode. Thank you again.

  • jadane

    An even easier way to get the stuff into the heater that I use often. If you have the tank drain prepared so that you can drain a quart of water or so, this will take 5 minutes. (1) Shut off cold water intake to tank. (2) open tank drain (you will lose a bit, not much, water, until vacuum stops it). (3) fill a quart jar with however much bleach/hydro peroxide you want in tank (I use a cup or so): I dilute it 3:1 (4) duct tape a short hose section to the most convenient hot water faucet you have and put the end in the quart jar. (5) open hot water faucet– the line will protest, then it will suck the entire contents of the jar through your system, into the heater (again the same amount of water will drain from the tank) (6) close faucet (7) close h/w tank drain and re-open inlet. (8) forget about it, and when you next use the hot water–3 hours? 8 hours? more, you’ll have a tankful of chorinated water that you can use however you normally use hot water. This takes 5 minutes: if you try to drain and refill tank, which is probably better, you make this simple procedure a complicated one.

    • Dan

      This worked like magic! After struggling and failing to get the anode loosened which was my “plan A” way to get the peroxide in the tank, I went to your method of using the vacuum to do the work. I duct taped a small vinyl tube to a closely hot water faucet, stuck the hose into a full 32 oz bottle of peroxide, turned on the hot water valve, and watched Mr. Thirsty do it’s thing. Thank you!

  • I’m not as informed on the cold water issues, but if it goes away after a couple minutes, that probably means there’s a buildup of sulphur-based gas somewhere “upstream.” Do any of your neighbors have this issue? Are you on a well?

    • Frustrated Donna

      We are not on a well. County water. Our neighbor had an issue right around the first day we started noticing the issue. They had the county come flush at the hydrant and haven’t had an issue since. I’m thinking there was a county issue with bacteria, that in turn hit our already volatile softener and destroyed our old anode rod. I believe the bacteria is built up in the lines around the area of the softener, but we are having difficulty getting peroxide into this area. Is there a better way to introduce the peroxide into the entire system? Would it be better to run through the hot tank or would that not even enter the problem area?

      • If you introduce it into the hot tank, it will only affect the hot water lines. Since you don’t have any type of cold-water storage tank, I don’t see how you’ll be able to introduce any significant amount of peroxide into the system. Your best bet is just to flush, flush, flush. 🙁

  • Phil

    My hot water heater only stinks when its on i turned. It off and the smell went away.my water does not stink at all.tje smell is only in the garage where the tank is

  • I just use the cheapo 3% drug store stuff. If you’re using the industrial strength 35% stuff, I’d use only an ounce per 10 gallons, or maybe even 3/4 oz. For for a 40 gal tank, I’d start out with 3-4 oz and see how it works.

  • If you’re certain other fixtures also use the same tank as the bathroom sink, and they have no smell, then yes… it’s a different issue. I’d check to see if something stinky is in the fixture.

  • Hi, Michael. All you should need is 1) room in the tank, and 2) gravity. Make sure you’ve drained the tank a bit so there’s room in the top, and also defeated any vacuum by opening a hot water faucet until it stops running. If there’s a rubber flap or something similar blocking the flow, try sticking a more narrow funnel tip down in there, or cobble together some small hose taped to a funnel and shove it in there.

  • PresyBoy

    Steve ….resolve some confusion. Your anode replacement rod suggestion recomends replacing existing with an aluminum / zinc rod. Your link takes me to Amazon and a magnezium rod. Are they the same. Thanks

    • Hi, PresyBoy. No, they are not the same. Maybe Amazon changed the product behind that link. Aluminum is generally what to try first if you have rotten egg smell.

  • Hi, Billy. Yes. hydrogen peroxide won’t hurt the septic. In fact, some experts recommend putting some in your septic system periodically to help it work better!

  • Hi, Susan. I’d bet either the chlorine or the peroxide would work. They’re both doing the same thing: killing the smelly bacteria. 🙂

  • Scott Johnson

    After i put in the hydrogen peroxide and let it sit for a couple of hours. do I have to drain it,or just start using the water again?

    • No, you don’t need to drain it. It’s perfectly safe.

  • JZ

    I purchased a house back in April 2013 and at the time I purchased a new filter and softener system for the house as the water had a strong rotten egg smell. A year later I had the issue with the hot water (rotten smell in hot water), and I resolved it by changing the anode rod every 6 months. Now two weeks ago I started getting the rotten egg smell in cold water only. I called the company that installed the systems and they did all the chemical tests in water and everything resulted in normal readings. So they recommended line chlorination because they said there might be bacteria growing in plumbing and it might be producing that rotten egg smell. Therefore, we agreed to try; but unfortunately 3 days after the chlorination the smell came back, but it came back even stronger. and again only the cold water. Then the next two days the water was fine without any smell and then it started all of a sudden. (Basically the smell comes and goes.) The strange thing is that I always go check outside to see if the water right after filter also stinks like rotten eggs, but it doesn’t. The smell is only inside the house, on showers and sinks.

  • No. Boiling water doesn’t get rid of sulphur smell. In fact, there are many natural hot springs in the world with REALLY hot water… and they smell really strong of sulphur. 🙂

  • Still the same. Most electric tanks also have an anode.

    • Michael H

      Steve, Im getting ready to replace the “ROD” and do the flush w/ peroxide any order to follow , like peroxide first then replace the ROD to prevent premature build up ? side cold water is starting to smell too , is it just bad stuff in the lines ? ( facts old home on a well with a softener system and a septic)

      • Once you’ve partially drained the tank and shut off the incoming water, it doesn’t matter what order you follow. Smell in the cold water is usually a sign of something in the lines, or something at the well source. Have you had the well water tested lately? Was the sulfur content high?

        • Michael H

          Test just the hardness and the ph, we live in a country duplex if you would and the water softener is in my neighbors basement and he wasn’t adding enough salt until I asked what was up with water he said even though it was his responsibility he was only adding when it was low as in water on of the salt, so I tried to tell him that was bad and to fill and I bought extra salt to make sure it was full so everything would be more efficient, it must be low again because the water was hard on the test strip… I will work on the Hot water heater smell and see if it improves thank you, can anything be added to the water softener to freshen it upossible?

  • Dorothy C

    Thanks Steve for you post. We had the rotten egg smell in out hot water only, with all 3 strikes against us. We poured the peroxide in the hot water tank and immediately the problem was fixed.

  • patrick

    Peroxide solution works great for me, I live in a 100 year old schoolhouse with well water.once a month I change the whole house canister water filter and add a bottle of peroxide into the canister, works every time, very simple.