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Short answer: For hydrogen water, ppm means milligrams of dissolved hydrogen gas per liter. At normal air pressure and room temperature, water holds only about 1.6 ppm; higher figures require pressure or a sealed container, and they fall once the water is opened [1][2]. Human trials have used roughly 0.5 to 15 ppm, and none has identified a best or minimum concentration, so a higher number on a label is not evidence of a bigger benefit.
What does ppm mean in hydrogen water?
It's a concentration: 1 ppm is 1 mg of hydrogen (H₂) in 1 liter of water [2]. Research papers often report millimolar (mM) instead; 1 mM of H₂ is about 2 mg/L, so the "saturated" level of 0.8 mM is about 1.6 ppm [1].
To estimate how much hydrogen you actually swallow, multiply the concentration by the volume: 0.5 liter at 1.6 ppm is about 0.8 mg of hydrogen. Our guide to how much hydrogen water per day lists the concentrations and daily amounts used in 16 human trials.
How high can the ppm go?
Water at normal pressure and room temperature is saturated at about 1.6 ppm [1]. Anything above that is supersaturated: it only holds while pressure keeps the gas in.
- In lab tests, sealed pressure-resistant bottles reached about 4.5–6 atmospheres inside and held roughly 7–10 ppm [2].
- Trials have used drinks made under pressure at 4–5 ppm [3], and magnesium-tablet drinks measured at more than 4 mg/L [4].
- The highest concentration we found in a human drinking trial was 15 ppm, at 0.5 liter a day [5].
A high figure on a label is usually measured at the factory or right after the device runs, not when you drink it.
What makes the ppm drop?
Opening the container. In one trial, freshly made water measured 5.4 mg/L and 4.2 mg/L one hour after the cap was opened [3]. In lab tests, pressurized bottles held their hydrogen for days while sealed, but levels fell significantly within an hour of opening [2]. Japan's National Consumer Affairs Center found that opened-and-recapped products fell to 30–60% of their starting hydrogen within 5 hours [6].
The container material. Hydrogen is a tiny molecule that passes through glass and plastic walls; aluminum holds it much better [1]. In a comparison of containers over 12 hours, aluminum and stainless steel lost very little hydrogen, while several plastic containers lost more [7]. In Japan's tests, two products sold in plastic bottles had no detectable hydrogen at all [6].
Time and handling. Pouring, shaking and warm temperatures all speed the gas's escape. Trials that measured concentration told people to finish each serving within minutes to an hour of opening (see the dose guide).
Is higher ppm better?
That hasn't been shown. Positive and negative trial results appear at both low and high concentrations:
- A trial at about 0.5 ppm found no clinical effect on its main outcome [8], while a 15 ppm trial reported changes in a few aging markers but not most [5].
- Only one trial compared two amounts directly, and the groups didn't differ significantly in how many people improved (details in the dose guide).
- Reviews have noted that the reported effects don't clearly increase with dose [9].
So "more ppm" is a claim about what's in the water, not about what it does for you. Our honest overview of the evidence is is hydrogen water a scam?
How can you check a ppm claim?
Measure hydrogen directly, and measure it when you'd actually drink it.
- Don't rely on ORP. Oxidation-reduction potential meters respond to pH and other factors, so they can't tell you how much hydrogen is in the water; reviewers advise against ORP-based hydrogen meters [10].
- Use a hydrogen-specific method. Redox titration reagent drops made for dissolved hydrogen, dedicated dissolved-hydrogen meters, or lab gas analysis measure H₂ itself [10].
- Test at drinking time. Measure right after opening or making the water, and again after the time you'd normally take to finish it.
- Ask for dated, independent results. A lab report that states the method, date and conditions is worth more than a number on a box. Japan's consumer center asked sellers to label a concentration guaranteed through the expiration date, not just "at filling" [6].
These checks apply to every product, including those sold by our funder.
What the evidence doesn't show
- No optimal ppm. No trial has identified a best or minimum effective concentration.
- Label ≠ glass. Most trials reported the concentration when the water was made, not when it was drunk, so even study doses are approximate.
- No proven dose-response. Higher concentrations haven't been shown to produce bigger or more reliable benefits [9].
- Safety data are short-term. Trials at these concentrations have been small and mostly weeks to months long; see hydrogen water side effects.
Frequently asked questions
What is a good ppm for hydrogen water?
No trial has identified a best concentration. Human trials have used roughly 0.5 to 15 ppm, and results were mixed at every level. What matters most for comparing products is the concentration at the moment you drink, measured with a hydrogen-specific method.
How long does hydrogen stay in water after opening?
It starts escaping as soon as the container is opened. In one measurement, water fell from 5.4 to 4.2 mg/L within an hour; Japanese consumer tests found opened-and-recapped products at 30–60% of their starting level after 5 hours. Drink it soon after opening.
Can water hold more than 1.6 ppm of hydrogen?
Only under pressure or in a sealed container. At normal pressure and room temperature, about 1.6 ppm is the saturation level; higher concentrations fall back toward it, and then lower, once the water is exposed to air.
Is glass or aluminum better for storing hydrogen water?
Aluminum. Hydrogen passes through glass and plastic walls, while aluminum holds it much better, and stainless steel also performed well in a container comparison. Plastic bottles lost the most, and some plastic-bottled products tested in Japan had no detectable hydrogen.
Sources
- Ohta S. Recent progress toward hydrogen medicine: potential of molecular hydrogen for preventive and therapeutic applications. Current Pharmaceutical Design. 2011. PubMed · Our summary
- Kurokawa R, et al. Convenient methods for ingestion of molecular hydrogen: drinking, injection, and inhalation. Medical Gas Research. 2015. PubMed · Our summary
- Ishibashi T, et al. Consumption of water containing a high concentration of molecular hydrogen reduces oxidative stress and disease activity in patients with rheumatoid arthritis: an open-label pilot study. Medical Gas Research. 2012. PubMed · Our summary
- Kura B, et al. Biological effects of hydrogen water on subjects with NAFLD: a randomized, placebo-controlled trial. Antioxidants. 2022. PubMed
- Zanini D, et al. The effects of 6-month hydrogen-rich water intake on molecular and phenotypic biomarkers of aging in older adults aged 70 years and over: a randomized controlled pilot trial. Experimental Gerontology. 2021. PubMed · Our summary
- National Consumer Affairs Center of Japan. Drinking "hydrogen water" in containers and made with generators: there is no official definition, and dissolved hydrogen concentrations vary (in Japanese). December 15, 2016. kokusen.go.jp
- Tanaka Y, et al. Dependencies of hydrogen-water on mineral-based hardness, temperatures and the container materials, and effects of the oral washing and drinking. Medical Gas Research. 2020. PubMed · Our summary
- Ito M, et al. Open-label trial and randomized, double-blind, placebo-controlled, crossover trial of hydrogen-enriched water for mitochondrial and inflammatory myopathies. Medical Gas Research. 2011. PubMed · Our summary
- Ohno K, et al. Molecular hydrogen as an emerging therapeutic medical gas for neurodegenerative and other diseases. Oxidative Medicine and Cellular Longevity. 2012. PubMed · Our summary
- LeBaron TW, et al. Electrolyzed-reduced water: Review II: safety concerns and effectiveness as a source of hydrogen water. International Journal of Molecular Sciences. 2022. PubMed · Our summary
Conflicts of interest in these sources: source 10's authors are affiliated with the Molecular Hydrogen Institute and H2 Analytics, a hydrogen-testing company that has certified products for Echo Technologies, which funds this site. Source 2 was written by scientists at a hydrogen-water company.
How we wrote this: corrected and rewritten on September 23, 2026, replacing an earlier version that included product promotion and claims we couldn't support. Drafted with AI assistance from the sources above and checked against each source by the Hydrogen Studies editorial team. This is general information, not medical advice.