How ozone treatment works
Ozone (O₃) is oxygen with a third atom attached, and that third atom is desperate to leave. It makes ozone one of the most powerful oxidants available for water treatment — considerably stronger than chlorine. An ozone system generates it on site from air or oxygen using an electrical discharge, dissolves it into the water, and lets it react.
When ozone meets a contaminant it oxidises it and then reverts to ordinary oxygen. Nothing is left behind but O₂. That is the technology’s headline appeal and, as the next section explains, also its central limitation.
What it does well is genuinely broad: inactivating bacteria, viruses and chlorine-resistant organisms; oxidising dissolved iron and manganese into filterable particles; and breaking down the compounds responsible for taste, odour and colour. Utilities also use it ahead of biofiltration, and because it does not chlorinate organic matter it produces fewer of the chlorinated by-products that chlorine creates. Ozone has been used in European municipal treatment since the mid-twentieth century, and the FDA granted it GRAS status for food contact applications in 1982.
The residual problem
This is the defining constraint, and it is the same lesson as UV treatment: ozone provides no residual protection whatsoever.
Ozone is unstable in water and readily volatilises out of it. Disinfection happens at the point of contact between ozone and water, and stops there. Nothing continues protecting the water downstream — not in your pipes, not in a storage tank, not overnight. Chlorine and chloramine exist in distribution networks precisely because they persist; ozone by design does not.
The practical consequence is that municipal ozone systems almost always add a secondary disinfectant — typically low-level chlorine or chloramine — after ozonation. Ozone does the heavy oxidation; something else maintains protection to the tap. Any domestic product implying ozone alone keeps water safe in a tank or plumbing run is describing something the chemistry does not permit.
Note also that protozoa are the hard case here, as they are for chlorine. Published guidance is explicit that Giardia and Cryptosporidium require substantially longer ozone contact time than bacteria — so a short-contact domestic unit that inactivates bacteria may not be achieving cyst reduction at all.
Bromate — the by-product that matters
Ozone is often marketed as the disinfectant that creates no by-products. That is not accurate. It creates different ones, and the important one is bromate.
Where source water contains naturally occurring bromide, ozone oxidises it, and on prolonged ozonation bromide progressively converts to the bromate ion. Bromate is a regulated contaminant with a health basis rather than an aesthetic one — the WHO guideline value and the US EPA maximum contaminant level both sit at 10 µg/L, Australian guidelines set a bromate limit, and US public water systems using ozone are required to monitor for it.
Controlling it is an active area of research rather than a solved problem. One published study on high-bromide water found monochloramine reduced bromate formation by about 80% and hydrogen peroxide by about 36%, with neither measurably harming virus or coliform inactivation — while also finding that maintaining an ozone residual was critical for the more resilient spore-forming organisms. In other words: the levers that suppress bromate and the levers that maximise disinfection pull against each other, and balancing them is an operator’s job.
The Australian relevance is specific. Bromide is elevated in saline-influenced and coastal source waters — which describes parts of Perth’s groundwater and Adelaide’s Murray-influenced supply. Bromide levels are not something a householder can see or taste, and a domestic ozone unit does no bromate monitoring at all.
The safety issue nobody advertises
Ozone is a toxic gas, and this is where domestic units differ most sharply from municipal plants. Published extension guidance is blunt: like chlorine, ozone is toxic, and generators may leak, creating an ozone hazard inside the home and causing illness.
Municipal installations manage this with engineered off-gas destruction, contactor design, ventilation, monitoring and trained operators. A domestic unit in a laundry has none of that. Ozone that leaves solution has to go somewhere, and in an enclosed space that somewhere is the room.
Worth separating clearly from water treatment: ozone generators sold as air purifiers are a different product with a poor safety reputation, and health agencies have warned against their use in occupied spaces. If a seller is offering one device for both water and room air, that alone is reason for caution.
Does it make sense in an Australian home?
On treated mains supply: almost never. Utility water is already disinfected and carries a residual specifically to keep it that way to your tap. Adding a technology whose defining weakness is that it leaves no residual, to water that already has one, addresses nothing — while introducing bromate risk and an in-home gas hazard.
On untreated supply: the case is real but narrow. For bore water with iron and manganese, ozone’s oxidising ability is genuinely useful — it converts dissolved iron and manganese into particles a filter can then remove, which is a job carbon cannot do. But it must be followed by filtration to capture what it has oxidised, and it does not substitute for a residual disinfectant on a storage system.
The comparison that usually decides it: for rainwater and bore supply, UV achieves microbiological inactivation with no by-products, no gas hazard and NSF/ANSI 55 certification available — a standard ozone has no domestic equivalent to. Ozone’s advantage over UV is oxidation of iron, manganese and taste compounds, not disinfection.
Our verdict on the evidence
Ozone is powerful, proven, industrially mainstream technology that scales down to the household badly. There is no scientific dispute about what it does — the oxidation chemistry is established, the municipal track record spans decades, and for iron, manganese, taste and colour it is genuinely excellent.
What does not transfer to a domestic setting is everything that makes it safe and effective at plant scale: bromate monitoring, off-gas control, contact-time design, trained operators, and a secondary disinfectant to carry protection downstream. Strip those away and you have a strong oxidant with no residual, an unmonitored regulated by-product, and a toxic gas generator in a laundry.
Our position: on Australian mains supply, ozone solves a problem you do not have. On bore water with iron or manganese it has a real and specific role — as an oxidiser feeding a filter, not as a standalone purifier — and even then, ask what the contact time is, whether off-gas is managed, what the source water’s bromide level is, and what maintains disinfection after the water leaves the unit. If the honest answer to the last question is “nothing”, that is the technology working exactly as designed, and it is why utilities pair it with something else.
Primary sources: UMass Amherst Center for Agriculture, Food and the Environment extension guidance on ozone treatment of drinking water supplies, including residual limitations, protozoan contact time and in-home gas hazard; Texas Commission on Environmental Quality guidance on ozone and bromate, including mandatory bromate monitoring for public water systems using ozone; WHO and US EPA bromate guideline and maximum contaminant level of 10 µg/L; peer-reviewed work on bromate control in ozone disinfection (Environmental Science & Technology), reporting ~80% and ~36% bromate reduction via monochloramine and hydrogen peroxide respectively and the importance of ozone residual for spore-forming organisms; FDA GRAS designation for ozone in food contact applications, 1982. Reviewed August 2026. FilterOut takes no commissions and carries no paid placements — see who to trust for filter advice.
FAQ
Does ozone leave anything in the water?
No — it reverts to ordinary oxygen after reacting, which is its main appeal. But that also means it provides no residual protection: disinfection stops at the point of contact and nothing continues protecting the water in your pipes or storage tank.
Is ozone treatment safe?
At municipal scale, yes, with engineered off-gas control and bromate monitoring. Domestically it carries two risks that plants manage and homes usually don’t: ozone is a toxic gas and generators can leak indoors, and where source water contains bromide, ozone forms bromate — a regulated by-product with a WHO and US EPA limit of 10 µg/L.
Is ozone better than UV for bore or rainwater?
For disinfection alone, UV is usually the better domestic choice — no by-products, no gas hazard, and NSF/ANSI 55 certification available. Ozone’s real advantage is oxidising iron, manganese and taste compounds, which UV cannot do — but it must be followed by filtration to remove what it has oxidised.