Skip to content


Chlorine or Hydrogen Peroxide – Which is Better for Treating Water?

by Mark Timmons June 09, 2021 15 Comments

The water treatment industry has used Chlorine (Cl2) for well over a hundred years. Chlorine gas was used in Belgium in 1903 to disinfect drinking water. In 1908, Jersey City, New Jersey, used the first liquid chlorine to disinfect water (sodium hypochlorite). In the 1950s, Eastern Europe was the first to use hydrogen peroxide (H2O2) for drinking water disinfection. H2O2 is known for its high oxidative and biocidal efficiency. Hydrogen peroxide has not been used often for drinking water disinfection, but its popularity seems to increase each year.

The use of chlorine in drinking water has always been prevalent since it first being introduced, and it remains popular. The linchpin for chlorine is that it is an excellent disinfectant. Chlorine is toxic to pathogens and very effective, but chlorine can be harmful not only for microorganisms but also for humans. Chlorine is an eye irritant to humans and an irritant to nasal passages and the human respiratory system. Chlorine is an excellent disinfectant but not a strong oxidizer, which is where H2O2 breaks from chlorine.

Hydrogen Peroxide

Hydrogen peroxide is a strong oxidizer. In fact, it is more potent than chlorine (Cl2), chlorine dioxide (ClO2), and potassium permanganate (KMnO4). Also, through catalysis, hydrogen peroxide can be converted into hydroxyl radicals (OH). This blog is not to say that one technology is better than the other, but rather to make you aware of what chlorine can and cannot do and understand what role the use of hydrogen peroxide can play in water treatment.

On major advantage that H2O2 has over chlorine is that it does not form Disinfection By-Products (DBP's) like trihalomethanes (THM) which are known carcinogens. Whenever chlorine is used, you must follow it with the correct amount of granular activated carbon (GAC) to remove the DBP's effectively. Hydrogen Peroxide, on the other hand, does not seem to produce such DBP's.

Water treatment professionals may have to change their thinking when comparing hydrogen peroxide to chlorine because they are two different animals. One is an excellent disinfectant (chlorine), but the other is a great oxidizer (hydrogen peroxide) and how they are utilized is dramatically different.

Chlorine requires contact time, which is typically 20 minutes for every gallon per minute of flow. Therefore, if you are flowing 10 GPM, you need 200 gallons of contact time (10 GPM x 20 minutes = 200 GPM). On the other hand, hydrogen peroxide is not a good disinfectant but rather an excellent oxidizer. It does not require contact time. Contact time only dilutes its ability to oxidize. Therefore, you do not want to use hydrogen peroxide with a retention tank.

Hydrogen Peroxide VS Chlorine

If you haven't already figured it out - hydrogen peroxide is not a good idea for disinfection; the same as chlorine is not a good idea for oxidation. If you have surface water and need to disinfect it, especially if there is algae, then chlorine is dramatically superior to hydrogen peroxide. However, if you have incredibly high iron or sulfur, chlorine is not a good choice, but hydrogen peroxide is. Removing iron and sulfur is best accomplished with oxidation, and H2O2 is an excellent oxidizer.

Just do not confuse oxidation and disinfection. The definition of disinfection is “the process of cleaning something, especially with a chemical, to destroy bacteria.” Oxidation, on the other hand, is different. The terms oxidation and reduction can be defined by adding or removing oxygen to a compound. Both reduction and oxidation coincide, so we call that a “redox reaction.”

As stated, hydrogen peroxide has the chemical formula H2O2 and is an oxidizing agent similar to oxygen in effect but is significantly more robust. The oxidizing activity of hydrogen peroxide results from the presence of the extra oxygen atom compared with the structure of water. I like to say that “Hydrogen peroxide is very forgiving.” What I mean by that is that (when applied correctly) extreme amounts of iron and hydrogen sulfide can be removed from the water supply effectively and consistently.

Many water treatment specialists have been involved in the pioneering of hydrogen peroxide technology… even before me. Still, in my 25+ years of using H2O2, I doubt that anyone has sold the vast number of systems that we have. I will be the first to admit that we made a lot of mistakes in the beginning. Among them are the following:

  • We used to use a contact tank or inject H2O2 ahead of a pressure tank - all that did was slow the oxidation process. Now we inject it just ahead of a catalytic carbon tank.
  • We used to use a static mixer - all that did was knock out some of the air bubbles and weaken the reaction. No static mixer is needed. In fact, a static mixer is counter-productive.
  • We used to use a flow switch to activate the H2O2 pump (or hook it up to the pressure switch so that it ran when the pump ran - now we use a meter and proportional injection system that injects the “precise amount” of H2O2 regardless of whether the flow is 1 GPM or 18 GPM.
  • We used to use regular hydrogen peroxide, which “decomposes” quickly - now we have it “stabilized” so that it does not decompose and remains at maximum strength for over a year.

We Still Have Love For Chlorine

It's not that we hate chlorine - it is necessary in many cases - but we prefer hydrogen peroxide for iron and sulfur eradication. The only drawback to a H2O2 system is that you will have an annual peroxide bill of $200 to $600/year, but that is insignificant to having amazing iron and sulfur-free water.

What about maintenance? Of course, all water is different, and water chemistry is vitally important. “Competing contaminants” can affect the efficacy of H2O2 as an oxidizer. Therefore, a detailed laboratory water analysis is paramount with H2O2, chlorine, or any other type of water treatment.

If you inject chlorine, I would advise you to become intimately acquainted with your chemical injection pump (or have someone on speed dial to service it) because chemical injection pumps typically have issues with chlorine. It degrades the rubber parts or tubes, necessitating repair and maintenance (typically a couple of times a year… if you are lucky). Additionally, chlorine frequently crystallizes at the “injection point,” also necessitating disassembly and cleaning of the injection fitting.

When injecting hydrogen peroxide, we always use a Stenner Peristaltic Pump because this type of pump injects much more consistently. The H2O2 does not cause issues with degrading the rubber parts or tubes. Additionally, it does not crystalize at the injection point. We have been using these pumps for 25+ years,

and it is not unusual for a pump to go 5 to 10 years without any maintenance. Zero!

Typically, the catalytic carbon in the tank needs replaced about every five years, but it could be more or less frequent… depending upon the water analysis and daily usage. Since we sell systems all over the United States, we need a technology that is very forgiving and nearly foolproof! Hydrogen Peroxide is generally the best solution for sulfur and high levels of iron. It's not perfect, but it is closer than any other technology found at a price that you can afford.

Overall, hydrogen peroxide is more expensive than chlorine and works best when iron and sulfur are present in the water supply. Since it works faster than chlorine, no contact tank is required. Additionally, H2O2 is effective at a more comprehensive pH range, meaning that it is more effective on more types of water.

Prev Post
Next Post


August 12, 2021 Clay

Good info. Wondering if you can expound on the idea that a retention tank with H2O2 is a detriment? How would a tank slow the oxidation process? If the H2O2 is injected inline B4 a tank, then the water would be oxidized at that point, then the tank would just be holding “cleaned” water until it is needed to be pushed onto the house via filtration, no?
We have a new low yield well and MUST have a 200 gallon holding tank. We will have a well pump (on float switch) and then a pressure tank after the holding tank utilizing a jet pump. Then filter downstream. We want the H2O2 to go inline just B4 the holding tank. Are we wrong? Thanks.

August 17, 2021 Mark Timmons

Yes, you are wrong because you are confusing oxidation with disinfection (which requires contact time). Since H2O2 is such a dramatically better oxidizer than Cl2, it does not need any contact time and for that reason alone, there is no reason to have contact time. However, of even greater importance is that since it is a better oxidizer, it needs a vehicle (Catalytic Carbon) to allow and facilitate this process to occur. It is our opinion that the catalytic carbon acts as a catalyst between the H2O2 and the Iron or Sulfur. To speed up the process, it is vitally important that the H2O2 is as potent as possible. using a retention tank simply dilutes the hydrogen peroxide and slows the process. Get rid of any rentention and you will use less peroxide and have dramatically better results!

September 23, 2021 Anthony Aziba

I think in some cases a retention tank may be required where there’s a high volume of iron in the water. Inline dosing may not suffice. The H202 treatment process may need more contact time to oxidize the iron in the water solution

November 06, 2021 Mark Timmons

No, that is not true. We have tested and verified this. Have you? The more iron you have, the more important it becomes not to dilute it. YOU NEVER NEED A CONTACT TANK. You may, however, need to add more H2O2.

November 18, 2022

Excellent keep up the good work

December 08, 2022 Nick tsironis

I have a home in Belize and use rain water roof collection stored in big plastic tanks 20,000L. Currently put 2 1/2 cups of bleach a month. But I am concerned about crypto and other spores.would peroxide be a better choice??

December 08, 2022 Mark Timmons

No, peroxide would not be better. I would chlorinate with 76% chlorine pellets like this: We have a system that we highly recommend that includes UV and “Zeta Charged Media,” which physically blocks crypto and giardia:

December 13, 2022 Jeff

Is peroxide system safe for dogs to drink and or pregnant dogs?

December 13, 2022 Mark Timmons

First of all, we do not recommend or approve of drinking hydrogen peroxide. We use hydrogen peroxide to treat water followed by catalytic carbon. There is no peroxide in the drinking water.

January 29, 2023 Bill

I just ordered a Flexx Infusion H2O2 system from you on 1/28/2023. Hasn’t arrived yet of course as it’s only one day later. The local water treatment company wanted to sell me an Ozone system. In order to maintain the warranty on their system they told me I had to have them come every year to replace some tube and do a cleaning and the cost to do that was $300 annually. I told them I was fully capable of doing the maintenance myself, and they said if I do that then I don’t get the warranty other than what the manufacturer offered for each component and I would need to deal with the manufacturer for any warranty claims.

The only thing that’s still bothering me is when I asked the local water treatment company about H2O2 systems they said they don’t recommend them because it’s not healthy to drink hydrogen peroxide. I said everything I had seen online indicated there was no actual hydrogen peroxide after the water went through the catalytic carbon backwashing tank. Hence no hydrogen peroxide in the drinking water. The sales person who I spoke to at US Water also assured me there’s no hydrogen peroxide in the drinking water as long as there is a properly operating catalytic carbon filter in place.

I could not get a straight answer from the local water treatment company as to whether or not they even sold H2O2 systems. I suspect they don’t since they were so quick to dismiss them.

I hope the H2O2 system works as well as claimed on your site and other sites I’ve seen. I don’t think I can take the sulfur smell much longer from my water. I flushed out my water tank and changed the anode rod and it still smells. I plan to sanitize my system with chlorine before installing the H2O2 system so that I’m hopefully starting with a system that has no issues.

If you have recommendations for sanitizing the interior pipes I’d appreciate it. Right now I do have one of those filter housings and a 5 micron filter after the pressure tank on my system. I know I could dump chlorine in my well head and do it that way. But I’d prefer to not dump the chlorine in my well. I was thinking about filling the filter housing with chlorine, running the faucets in the house till I smell chlorine and then filling the filter housing again and doing the same. Just not sure how much chlorine would be needed.


January 30, 2023 Mark Timmons

I was one of the pioneers into Hydrogen Peroxide Technology in residential water treatment, nearly 30 years ago. Over the years I have learned a lot about it, but these things still hold true. 1. Ozone is an excellent way to remove sulfur odor, but few companies do it properly and the results are spotty, at best. To do ozone right would generally cost 3X to 4X what a hydrogen peroxide system costs. 2. If you want an ozone system, we can design one and you can install it yourself, but the cost is generally prohibitive. 3. Hydrogen Peroxide is composed of the Elements of Water (H2O2) and is used as an oxidizer to oxidize iron and sulfur. When H2O2 acts as an oxidizer it oxidizes the iron and sulfur while being consumed in what is called the “REDOX” process. Since Hydrogen Peroxide is composed of the elements of water, hydrogen and oxygen, what little may be left over is removed by the Catalytic Carbon and even if it were not, it reverts back to H2O. 4. It is not healthy to drink H2O2 (at least in high concentrations), but the H2O2 is no longer in the water supply after the REDOX process. Whoever told you that is ignorant of the proesss. Your idea of how to sanitize with chlorine is both logical and effective. I would use this chlorine (below), which is much stronger than bleach (bleach is 5% while this is 70%). A couple of tablespoons in the sump and then filling it with water is the best method.

March 26, 2023 BOB

I came here to learn about the different systems. There are some good questions on this page but how come there are no answers from you??

April 11, 2023 Mark Timmons


May 31, 2023 David

I use a 1000lt water tank to provide water to my laying chickens. The water is harvested off a galvanised metal roof. Should I use hydrogen peroxide to sanitise the water. If so at what concentration?

June 19, 2023 Mark Timmons

Hydrogen Peroxide is a great oxidizer, but not a good disinfectant. Chlorine is a better disinfectant, but I would consider UV instead, possibly using this:

Leave a comment

Please note, comments need to be approved before they are published.

Someone recently bought a
[time] ago, from [location]

Thanks for subscribing!

This email has been registered!

Shop the look

Choose Options

Edit Option
Back In Stock Notification
this is just a warning
Shopping Cart
0 items