Aqueous ozone is water, usually tap water, containing a small amount of dissolved ozone (O₃). It is made on the spot, reacts with dirt and odour molecules and then reverts to water and oxygen.
If you organise the cleaning of a restaurant, hotel, office building or care facility, you probably have questions about it. How does the ozone get into the water? Why can't you store aqueous ozone? And what can and can't you use it for?
This article explains how aqueous ozone works, how it is made and how long it stays active. You will also see where its limits lie: for baked-on grease, limescale and periodic maintenance, you still need other products. After that comes a comparison with the ozone generator and pure water (water purified by reverse osmosis), followed by examples from hospitality, facility management and care, and five steps to get started.
What exactly is aqueous ozone?
Aqueous ozone, sometimes called ozonated water, is water in which ozone has been dissolved. Ozone is a form of oxygen. Ordinary oxygen, like the oxygen in the air, consists of molecules made up of two oxygen atoms: O₂. An ozone molecule has three: O₃.
That extra atom makes ozone less stable than ordinary oxygen. As a result, it reacts more readily with other substances, breaking down to O₂ in the process.
Aqueous ozone contains very little ozone. According to Enozo, the concentration in EnozoPRO is about 1 ppm (parts per million), or 0.0001%. That is one part ozone to a million parts water.
Ozone is a strong oxidiser. Oxidation means that one substance takes electrons from another, which changes that other substance. Chemists express this strength as the standard reduction potential, measured in volts. The higher the number, the stronger the oxidiser. The reference tables from LibreTexts (accessed on 3 November 2026) give these values:
- ozone (O₃): 2.07 V
- hydrogen peroxide (H₂O₂): 1.763 V
- oxygen (O₂): 1.229 V
Of these three, ozone is therefore the strongest oxidiser. The number describes the tendency to oxidise. It does not tell you how quickly a particular stain will come off: that also depends on the type of dirt, the contact time and the work done with the cloth.
How is aqueous ozone made?
There are two ways to make aqueous ozone. Either a device produces ozone gas from air and dissolves that gas in water, or the ozone forms directly in the water through electrolysis.
Ozone from air. Many devices first produce ozone gas from the surrounding air using an electrical discharge. They then dissolve that gas in water. The process therefore has two steps: making the gas and getting the gas into the water.
Electrolysis with a diamond electrode. In the second route, the ozone forms in the water itself. An electric current passes through an electrode in the water. At the surface of that electrode, some of the water molecules are converted into ozone. One material suited to this is diamond containing a small amount of boron: boron-doped diamond, or BDD for short. Researchers at the University of Warwick describe BDD as stable, with a wide potential window for this application (Wood et al., Journal of The Electrochemical Society, 2022).
Limescale is a point to watch. According to research by the German institute DECHEMA, diamond electrodes can build up limescale in water that is high in calcium and magnesium. Where tap water is hard, descaling and maintenance therefore deserve attention. For any device, check which maintenance the manufacturer recommends.
How EnozoPRO works. EnozoPRO takes the second route. It is a 400 ml spray bottle with a patented diamond electrode, the ADEPT diamond cell. Every time you pull the trigger, the cell makes fresh aqueous ozone from the tap water in the bottle. Nothing is mixed, dosed, stored or stabilised. You simply fill the bottle at the tap, and Enozo states that one bottle lasts 5,000 refills. You can read more about the diamond cell on the page about the technology behind EnozoPRO.
There is a practical reason for making it at the point of use: dissolved ozone breaks down quickly. If you make aqueous ozone in advance and store it, you will mostly be using plain water later on. A bottle that makes fresh aqueous ozone with every spray delivers the ozone to the surface only at the moment it is needed. And nobody has to measure or mix anything.
How long does aqueous ozone stay active?
Aqueous ozone stays active for minutes, not hours. Dissolved ozone breaks down to oxygen on its own, and in tap water that happens quickly.
Exactly how quickly depends on the water: temperature, pH, alkalinity and dissolved substances all play a part (Gardoni et al., Ozone: Science & Engineering, 2012). Warmer water and a higher pH speed up the breakdown, and substances dissolved in the water use up ozone. Tap water contains more dissolved substances than distilled water, so ozone disappears faster in tap water.
An undergraduate thesis by Silas Modesto de Melo at the Universidade Federal de Viçosa (Brazil, 2024) shows how large that difference can be. At 5 to 25 °C, the half-life of dissolved ozone was about 1.7 to 3.0 minutes in tap water and 56 to 169 minutes in distilled water (UFV, 2024, in Portuguese). The half-life is the time it takes for half of the ozone to break down. This was a single test set-up, so treat the figures as an illustration rather than a fixed rule.
For EnozoPRO, Enozo states an active half-life of about 5 minutes. After use, the ozone breaks down to oxygen (O₂); what remains is water and oxygen.
For daily cleaning, this leads to a simple way of working:
- Use aqueous ozone fresh for each task. There is little point in preparing a bucket of aqueous ozone for the whole shift. To put a number on it: with a half-life of 5 minutes, about an eighth of the ozone is left after a quarter of an hour.
- Don't store it. Aqueous ozone kept in a bottle or jerrycan is soon little more than water.
- Spray just before wiping. A bottle that makes fresh aqueous ozone with every pull of the trigger delivers the ozone at the moment you clean the surface.
How does aqueous ozone clean?
Aqueous ozone cleans through two mechanisms that work together. According to Enozo, the ozone reacts with dirt and odour molecules on the surface, and a microfibre cloth picks up the dirt mechanically.
As an oxidiser, ozone can react with molecules in the dirt or in a source of odour on the surface. This changes the structure of those molecules. The ozone itself breaks down to oxygen in the process, so no chemical residue is left behind.
Aqueous ozone contains no soap, so it does not loosen dirt the way a soap-based all-purpose cleaner does. The microfibre cloth takes over that role: its fine fibres pick up the dirt and hold on to it. Without a cloth, the dirt stays where it is. With visible dirt, wiping with a cloth is therefore always part of the job.
Fill the bottle with tap water, pull the trigger, spray and wipe with a clean microfibre cloth.
What "no residue" means. Many common cleaning products contain soap, fragrances or dyes. Whatever is left of them on the surface can cause streaks or form a sticky film. A film like that holds on to new dirt, so tables, glass and door handles get dirty again more quickly.
Aqueous ozone has no added fragrances or dyes and leaves no residue that attracts dirt. What goes on the surface is water with a little ozone, and that ozone breaks down to oxygen. No soap film is left behind to cause streaks or a sticky layer.
The water itself is still ordinary tap water, though, with the minerals it contains. Dry glass and mirrors afterwards with a dry microfibre cloth, so that no film of water is left to dry on them.
What can aqueous ozone do?
Aqueous ozone is suitable for the daily cleaning of hard, non-porous surfaces. Typical examples are tables, door handles, kitchen worktops, bathrooms and washrooms, fitness equipment, mirrors and windows.
Hard, non-porous surfaces do not absorb moisture. The aqueous ozone therefore stays on the surface, where the microfibre cloth picks it up again along with the dirt. The table below shows, for each surface or task, where aqueous ozone fits.
| Surface or task | Suitable for aqueous ozone? | Note |
|---|---|---|
| Tables and desks | Yes | Wipe daily with a microfibre cloth. |
| Door handles and grips | Yes | Spray onto the cloth and wipe all the way round the handle or grip. |
| Kitchen worktops | Yes, for everyday dirt | Heavy or baked-on grease needs a degreaser. |
| Bathrooms and washrooms | Yes, for everyday dirt | Limescale needs a limescale remover from time to time. |
| Fitness equipment | Yes, the hard parts | For example handles and frames; spray onto the cloth. |
| Mirrors and windows within reach | Yes | Dry afterwards with a dry microfibre cloth. |
| Porous or untreated surfaces | Test first | Test on an inconspicuous spot before using it more widely. |
| Baked-on grease and limescale | No | Use a degreaser or limescale remover (see below). |
Because one bottle covers every task marked "Yes" in the table, a cleaner needs fewer different bottles on the trolley. According to Enozo, EnozoPRO replaces a large share of the usual products in daily cleaning. Only tap water goes into the bottle, so you don't buy in concentrate refills and you are left with less packaging waste. You can read more about the bottle itself on the EnozoPRO product page.
What can't aqueous ozone do?
Aqueous ozone does not replace every cleaning product. For heavy or baked-on grease, limescale, porous or untreated materials and periodic deep cleaning, you still need other products or methods.
- Heavy or baked-on grease. Extractor hoods, ovens and fryer areas are typical examples. Aqueous ozone contains no soap or solvent to loosen thick layers of grease. Use a heavy-duty degreaser there.
- Limescale. Limescale is a mineral that dissolves in acid. Oxidation does not help with that. For limescale on taps, tiles and shower screens, you still need a limescale remover.
- Porous or untreated surfaces. Materials such as untreated wood absorb moisture. Test aqueous ozone on an inconspicuous spot first.
- Periodic deep cleaning. Stripping floors and applying fresh polish, deep-cleaning grout or large descaling rounds call for their own products and machines.
- Prescribed products. If the law, a protocol or your work instructions prescribe a specific product for a task, you still need that product.
Not everyone in the industry is convinced by ozone. In a 2024 article on Facto, the VSR, a Dutch cleaning-industry association, is sceptical. Ozone "is not a cleaning agent" ("geen reinigingsmiddel"), the association says in the article (Facto, 2024, in Dutch).
The criticism is partly justified. Aqueous ozone contains no soap and does not loosen grease the way an all-purpose cleaner does. It works together with mechanical action: the ozone reacts with dirt and odour molecules, and the microfibre cloth picks up the dirt. For tasks that call for a degreaser or limescale remover, aqueous ozone is no substitute. It belongs in the daily round, alongside the products for periodic work.
A simple schedule helps you keep daily and periodic work apart:
| Task | Daily | Periodic |
|---|---|---|
| Tables, desks and door handles | Aqueous ozone and a microfibre cloth | As set out in your work instructions |
| Kitchen worktops | Aqueous ozone and a microfibre cloth | Heavy-duty degreaser for baked-on grease |
| Bathrooms and toilets | Aqueous ozone and a microfibre cloth | Limescale remover for limescale build-up |
| Mirrors and glass within reach | Aqueous ozone, dried with a microfibre cloth | Glass at height: pure water with a telescopic pole |
| Fitness equipment | Aqueous ozone on the hard parts | Maintenance as recommended by the manufacturer |
| Floors | As set out in your work instructions | Periodic floor treatment with dedicated products |
| Tasks with a prescribed product | The prescribed product | The prescribed product |
Aqueous ozone, ozone generator or pure water?
Aqueous ozone, an ozone generator and pure water are three different techniques, each with its own purpose. Aqueous ozone is meant for surfaces, an ozone generator works through the air in a room, and pure water is meant for glass that has to dry without spots.
| Technique | What it is | What it is for | How you use it |
|---|---|---|---|
| Aqueous ozone | Water with a small amount of dissolved ozone, made fresh at the point of use | Daily cleaning of hard, non-porous surfaces | Spray onto the surface or the cloth and wipe with a microfibre cloth |
| Ozone generator | A device that produces ozone gas and releases it into the air of a room | Treating a room through the air, not a surface with a cloth | Position the device and run it according to the manufacturer's instructions |
| Pure water | Water forced through a membrane that holds back salts and minerals | Windows and glass that need to dry without spots, including at height | With a telescopic pole, up to about 15 metres high |
Aqueous ozone and an ozone generator share the word ozone, but they work in different ways. An ozone generator releases ozone gas into the air of a room. Aqueous ozone is ozone dissolved in water, which you use on a surface with a cloth. If you are searching for an ozone generator, you are looking for a different technique altogether.
Aqueous ozone and pure water are more often compared with each other, especially for glass. In reverse osmosis, water is forced through a membrane that holds back salts and minerals. As a result, a film of this water dries on glass without leaving spots. Window cleaners use it with telescopic poles up to about 15 metres (Facto, 2024, in Dutch). The membrane holds back calcium, magnesium, iron, sodium and potassium (Facto, 2025, in Dutch).
With pure water, what matters is what has been taken out: the salts and minerals. With aqueous ozone, what matters is what has been temporarily added: a small amount of ozone that reacts with dirt and odour molecules. The minerals from the tap water simply remain in it. As a result, pure water can be left to dry on glass, whereas after aqueous ozone you dry with a cloth. For glass at height, pure water is the obvious choice. For mirrors and windows within reach, aqueous ozone fits into the daily round.
You will also come across products sold as stabilised ozonated water with a long shelf life. That is a different concept from aqueous ozone made at the point of use. Given the short half-life of dissolved ozone in tap water, it is worth asking the supplier of such a product what is still in the bottle after storage, and how that was measured.
Where is aqueous ozone used?
Ozone is nothing new in the Netherlands: drinking water companies use it in their treatment process. Aqueous ozone for the daily cleaning of surfaces is a different application of the same substance.
One Dutch example comes from the Amsterdam water company Waternet (in Dutch). One of its treatment steps is literally called "Schoonmaken met ozon" ("cleaning with ozone"). According to Waternet, the ozone in that step breaks down small traces of substances such as medicines, and it makes the water taste better.
Inside buildings, daily cleaning looks different from sector to sector. The same principle applies everywhere: aqueous ozone for the daily round on hard surfaces, and specific products for periodic and prescribed work.
Hospitality and hotels
In hospitality venues and hotels, daily cleaning revolves around tables, the bar, door handles, mirrors and toilets. Hotel rooms add desks, bedside tables and bathrooms, and a hotel gym adds fitness equipment. For these tasks, aqueous ozone with a microfibre cloth can replace a large share of the usual sprays.
Other products are still needed for the heavy jobs. These include degreaser for extractor hoods, ovens and fryer areas, limescale remover for taps and showers, and products prescribed for a particular task. You can read more about this use on the page about aqueous ozone in hospitality and hotels.
Cleaning contractors and facility management
In offices and other buildings, the daily round covers desks, tables, door handles, kitchenettes, washrooms, mirrors and glass doors. A cleaner can get through those tasks with one bottle and a microfibre cloth, instead of several different bottles. Staff don't have to mix or dose anything, and there is less packaging waste.
Periodic floor maintenance, glass at height and descaling bathroom fixtures remain separate tasks with their own products and methods. For a cleaning contractor, that is also a planning question: which tasks belong in the daily round, and which in periodic maintenance? There is more on this on the page about cleaning in facility management.
Care settings
In care settings, aqueous ozone is intended only for the daily cleaning of non-critical surfaces. For example, tables, door handles, worktops, mirrors and windows in offices, corridors, reception areas and communal areas.
Aqueous ozone does not replace protocols that prescribe a specific product for a task. Involve your organisation's infection prevention specialist before you change the cleaning routine. Together, you decide which daily tasks qualify. In care settings, too, limescale removers and degreasers are still needed for periodic work. Read more about aqueous ozone in care settings.
How to get started with aqueous ozone
Start with a small, measurable step: choose a few daily tasks, test them on one site and then compare consumption and costs.
- Map your current products and tasks. Note which products you use, for which tasks and how much you buy each month.
- Choose the daily tasks that fit. Start with the hard, non-porous surfaces from the tables above. Leave periodic work and prescribed products out of it.
- Test for a few weeks on one site. Choose, for example, one floor, one restaurant or one department. If you are unsure about a material, test on an inconspicuous spot first.
- Brief your staff. Fill the bottle at the tap, spray onto the cloth and wipe with a microfibre cloth. Also explain why aqueous ozone is not prepared in a bucket in advance and why it does not smell of perfume.
- Compare consumption and costs. Set the consumption during the test period against the figures from step 1. You can make an initial calculation with Enozo's cost calculator.
Enozo can demonstrate EnozoPRO on your own surfaces, so you can see how it works before you start step 3. To arrange this, you can request a demo.
Frequently asked questions
Is aqueous ozone the same as ozone?
No. Ozone (O₃) is a gas, and aqueous ozone is water in which a small amount of that gas has been dissolved. In EnozoPRO, that is about 1 ppm. You use aqueous ozone on a surface with a cloth. An ozone generator releases ozone gas into the air of a room; that is a different technique.
What does aqueous ozone smell like?
Enozo describes the smell as fresh, "like the air after a thunderstorm". Aqueous ozone contains no added fragrances or dyes, so no perfume scent is left behind on the surface.
Can you store aqueous ozone?
No, there is little point. In tap water, dissolved ozone has a half-life of minutes, not hours. Stored aqueous ozone is mostly just ordinary water after a short time. Aqueous ozone is therefore best made at the point of use.
Can you make aqueous ozone yourself?
Yes, but only with a device that produces ozone and gets it into water. That can be done with ozone gas made from air and then dissolved in water, or through electrolysis directly in the water. EnozoPRO uses electrolysis: you fill the bottle with tap water and the diamond electrode makes fresh aqueous ozone with every pull of the trigger.
Does aqueous ozone replace all your cleaning products?
No. According to Enozo, aqueous ozone replaces a large share of the usual products in daily cleaning. Periodic tasks still call for specific products, such as limescale removers, heavy-duty degreasers and products required by law. You will find more answers in the frequently asked questions about EnozoPRO.
In summary
- Aqueous ozone is water, usually tap water, containing a small amount of dissolved ozone. That ozone reacts with dirt and odour molecules and then breaks down to oxygen.
- Dissolved ozone stays active for minutes, not hours. That is why you make aqueous ozone fresh at the point of use and don't store it.
- Used with a microfibre cloth, aqueous ozone fits into the daily cleaning of hard, non-porous surfaces, without residue that attracts dirt.
- Limescale, baked-on grease, porous materials and tasks with a prescribed product still need their own approach.
About this article: author Tom de Koster, Head of Research & Development at Enozo. Based on Enozo's product information and the sources linked in the text. More about the team behind Enozo. Last reviewed on 3 November 2026.
Written by Tom de Koster, Head of Research & Development at Enozo.
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