Ozone Water Is an Effective Disinfectant for SARS-CoV-2

Background: the search for safer surface and water disinfection during COVID-19

The COVID-19 pandemic created an urgent, everyday need for disinfectants that could reduce the spread of SARS-CoV-2 on surfaces and in water. Many of the chemical disinfectants used at scale - such as chlorine-based agents and alcohols - are effective but can leave residues, irritate skin and airways, or create by-products that are harmful to the environment. Ozone dissolved in water has long been used in water treatment because it is a powerful oxidant that breaks down quickly into oxygen, leaving no lasting residue. Researchers based in Wuhan, China, set out to test whether ozonated water could inactivate SARS-CoV-2 itself under controlled laboratory conditions.

Study design: testing ozonated water against live SARS-CoV-2 in the laboratory

This was a laboratory (in vitro) disinfection experiment, published as a research letter in the journal Virologica Sinica. The team prepared water containing measured concentrations of ozone - 36, 18, 9 and 4.5 mg/L - and mixed small volumes of a live SARS-CoV-2 viral solution with the ozonated water for short contact times, typically around one minute and up to ten minutes. After exposure, they measured how much infectious virus remained using two complementary methods: a plaque assay on Vero E6 cells, which counts virus particles still able to infect and kill cells, and quantitative reverse-transcription PCR (qRT-PCR), which detects the amount of viral genetic material present. Comparing treated samples against untreated controls allowed the researchers to judge how effectively the ozonated water had inactivated the virus.

Findings: ozone at 18 mg/L and above cleared the virus within a minute

At ozone concentrations of 18 mg/L and 36 mg/L, the treated samples showed complete inactivation of SARS-CoV-2 within one minute, with no detectable infectious virus in the plaque assay and no measurable viral RNA. At a lower concentration of 9 mg/L, inactivation was only partial: measurable viral RNA (roughly 4.0 x 10^3 to 5.0 x 10^5 copies/mL) and a small amount of infectious virus (about 1.0 x 10^2 to 7.0 x 10^2 plaque-forming units/mL) remained after exposure. This pattern pointed to a concentration threshold, with the authors reporting that ozone above 18 mg/L could eliminate SARS-CoV-2 infectivity within one minute.

What the authors concluded

The authors concluded that ozonated water is an effective disinfectant for inactivating SARS-CoV-2 in the laboratory, provided the ozone concentration is high enough. They highlighted practical advantages over some traditional chemical disinfectants: ozonated water is quick-acting, and the residual ozone decomposes back into oxygen within a short period - typically within about 30 minutes under normal conditions - so it leaves no lasting chemical residue and poses little secondary hazard to the environment. On this basis, they suggested ozonated water could be a useful, eco-friendly option for disinfecting surfaces and water where the virus may be present.

Limitations of this study

This was a small, early laboratory study reported as a short research letter, and its findings should be read with that in mind. The experiments were carried out in vitro, using virus mixed directly into ozonated water, rather than on real-world surfaces, textiles or skin where organic matter and material properties can reduce ozone's effectiveness and change the concentrations needed. The study tested a limited set of concentrations and contact times and did not assess practical questions such as material safety, the stability of ozonated water during storage and use, or the safe handling of ozone at these concentrations. Importantly, this study concerns the disinfection of surfaces and water. It does not examine ozone or ozonated water as a treatment for COVID-19 or any other infection in people, and it says nothing about breathing in ozone or applying it to the body. Ozone gas is a respiratory irritant and should not be inhaled. Any use of ozone for health-related purposes is a complementary approach and should always be discussed with a qualified healthcare professional.