Plasma-Activated Water (PAW)

Plasma-activated water is water that has been treated by exposure to a non-thermal plasma discharge, acquiring dissolved reactive species and a changed acid–base and redox character. It is the central subject of the source dossier recorded at Plasma-Activated Water: A source Dossier (Provisional Record), though that capture is incomplete and supplies no specific claims.

How it is produced

The general method is to bring a cold atmospheric plasma — an ionized gas near room temperature, generated by electrical discharge — into contact with a water surface or to bubble plasma-processed gas through water. Species formed in the gas phase cross into the liquid, where they dissolve and react. The discharge itself is described on Non-Thermal Plasma (Cold Atmospheric Plasma); the electrical-discharge basis connects the topic to electricity and physics.

What changes in the water

Three families of change are commonly described:

• Dissolved reactive species. Plasma treatment introduces reactive oxygen and nitrogen species (RONS) into the liquid. Typical members of this family include hydrogen peroxide, nitrite, nitrate, and peroxynitrite-related species. See Reactive Oxygen and Nitrogen Species (RONS).
• pH shift. When nitrogen oxides dissolve, they form nitrous and nitric acid, tending to lower the pH. The resulting acidity is part of what distinguishes PAW from untreated water.
• Redox potential. The pool of oxidising species raises the oxidation–reduction potential of the liquid.

Because the reactive species are short-lived, PAW is generally discussed as a freshly prepared treatment whose properties decay with time and storage.

Why it is of interest

The properties above are the reason PAW is studied in contexts where a short-lived, chemically active aqueous medium is useful — for example surface decontamination and agricultural treatment. The agricultural framing is recorded separately as Plasma Agriculture. This wiki does not, on the basis of the present source, assert any particular efficacy for any of these uses.

Evidence status

This concept page describes the subject as it is generally understood. It does not report results from the source dossier, because the ingested capture of that dossier contains no verifiable claims, no device specifications, and no trial data. Any efficacy attributed to PAW in archive material should be treated as a claim to be attributed, not a finding to be relied upon; see Patent as Evidence for the parallel caution about patent citations.

A caution about published kill rates

A 2026 methodological paper argues that long-lived hydrogen peroxide and ozone keep acting on bacteria after treatment ends, so antibacterial figures obtained without a chemical neutralization step are likely to be overestimates; it reports that most of the earlier studies it surveyed omitted that step. See The Neutralization Problem: Why Plasma-Activated Water Kill Rates May Be Overstated.

Tap water as a counter-example on pH

The acidification described above is not universal. A 2018 study of Paris tap water treated for up to 30 minutes by a dielectric barrier discharge reports that pH only slipped from 7.8 to 7.6, while nitrate rose from 0.86 ± 0.09 mmol/L to 3.55 ± 0.42 mmol/L and bicarbonate fell from 4.13 ± 0.09 mmol/L to 0.98 ± 0.25 mmol/L; the authors found the clearest signature of treatment in electrical conductivity instead. See What Plasma Does to Tap Water: Sixteen Measured Species, a Conductivity Check and a Lentil Trial (Judée et al., 2018).

Additives that change the result

A 2025 laboratory study reports that adding 10–100 μM potassium iodide to spark-generated, peroxide-rich PAW gave complete kills of E. coli and Listeria monocytogenes within minutes, but only partial inactivation of Salmonella enterica; its proposed hypoiodous acid mechanism is, by the authors' own account, not yet verified. See Adding Iodide to Plasma-Activated Water: Faster Kills, a Proposed Hypoiodous Acid Mechanism, and a Salmonella Exception (McClenaghan et al., 2025).

Viruses

A 2018 laboratory study reports that water treated by an argon-rich surface discharge inactivated the bacteriophages T4, Φ174 and MS2, kept most of its activity after 10 days at 22°C, and acted mainly through singlet oxygen; no human or animal viruses were tested. See Singlet Oxygen as the Virus-Killing Agent: Plasma and Plasma-Activated Water Against Three Bacteriophages (Guo et al., 2018).

Food and produce washing

A 2021 review of laboratory studies reports reductions of about 0.5 to 2.3 log when PAW is used as a wash on fruit and vegetables. Its larger figures come from pairing PAW with mild heat. The authors list lab-only data, cost, residual species and biofilm resistance as open problems. See Washing Produce with Plasma-Activated Water: A 2021 Review of Reported Kills, Mild-Heat Pairings and Open Gaps (Soni, Choi and Brightwell).

Related

• Washing Produce with Plasma-Activated Water: A 2021 Review of Reported Kills, Mild-Heat Pairings and Open Gaps (Soni, Choi and Brightwell) — a 2021 review of PAW as a produce disinfectant, alone and with mild heat.
• Singlet Oxygen as the Virus-Killing Agent: Plasma and Plasma-Activated Water Against Three Bacteriophages (Guo et al., 2018) — bacteriophage inactivation and the case for singlet oxygen.
• Adding Iodide to Plasma-Activated Water: Faster Kills, a Proposed Hypoiodous Acid Mechanism, and a Salmonella Exception (McClenaghan et al., 2025) — iodide as an enhancer of PAW against food pathogens and biofilms.
• What Plasma Does to Tap Water: Sixteen Measured Species, a Conductivity Check and a Lentil Trial (Judée et al., 2018) — sixteen species quantified in plasma-treated tap water, with a conductivity model.
• The Neutralization Problem: Why Plasma-Activated Water Kill Rates May Be Overstated — a critique of how PAW's antibacterial effect is measured.
• Non-Thermal Plasma (Cold Atmospheric Plasma) — the discharge that produces PAW.
• Reactive Oxygen and Nitrogen Species (RONS) — the proposed active agents.
• Plasma Agriculture — the application area.
• water, chemistry, agriculture — broad subject guides.