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Short answer: Hydrogen water is ordinary drinking water with extra hydrogen gas (H2) dissolved in it, much as carbon dioxide is dissolved in soda water. Water can hold only a little of this gas: about 1.6 parts per million (ppm) at normal air pressure and room temperature, and it escapes over time [2][7]. Scientists have studied molecular hydrogen since a 2007 study in cells and rats suggested it might act as a selective antioxidant [1]. How it works in the body is still debated, and the human evidence is limited and mostly small-scale.
What exactly is hydrogen water?
Hydrogen water is water that contains dissolved molecular hydrogen: H2, a molecule made of two hydrogen atoms. The water itself doesn't change. It is still H2O, and the hydrogen molecules simply sit among the water molecules as a dissolved gas [7]. You'll also see it called hydrogen-rich water, hydrogenated water, H2 water or molecular hydrogen water. All of these names mean the same thing.
What hydrogen water is not:
- Not a new kind of water molecule. Some marketing describes "H3O" or "H4O2" water. Dissolved hydrogen doesn't combine with water that way. It stays H2, surrounded by ordinary H2O [7].
- Not the same as alkaline or "ionized" water. Alkaline water is defined by its pH. Hydrogen water is defined by its dissolved gas. Some electrolysis machines, sold as water ionizers, make water that is both alkaline and contains some hydrogen, which is why people mix the two up. Researchers who traced the studies on that water concluded that its dissolved hydrogen, not its high pH, explains the effects reported in lab and animal studies [5][7]. For more, see hydrogen water vs. alkaline water.
How much hydrogen can water hold?
Not much. At sea-level pressure and room temperature, water is saturated at about 0.8 millimoles of H2 per liter. That works out to roughly 1.6 mg per liter, or 1.6 ppm [2][3][7]. Chemistry reference data give the same figure [13]. Put another way, a fully saturated liter holds about 19 mL of hydrogen gas [10].
So yes, hydrogen does dissolve in water, but only slightly. Carbon dioxide, the gas in soda, is roughly 40 times more soluble, molecule for molecule [13]. Cold water holds a little more hydrogen than warm water [13]. Ordinary water sitting in open air contains almost none: less than one-millionth of a milligram per liter [7].
Why some labels show higher numbers. How much gas water holds rises with pressure [13]. Water can therefore briefly carry more than 1.6 ppm if hydrogen is pushed in under pressure or made inside a closed container. Makers of tablets, electrolysis devices and ready-to-drink products often claim 2 ppm or more, and some claim over 7 ppm [10]. Those are manufacturer figures. Any gas above the saturation level will leave the water once it is back at normal pressure.
Hydrogen escapes. Dissolved H2 tends to leave water over time. It also passes through glass and plastic container walls, while aluminum containers hold it much longer [2]. In practice, that means drinking hydrogen water soon after it's made or opened. Our guide to ppm levels covers concentration in more detail.
Quick glossary
| Term | What it means |
|---|---|
| ppm | Parts per million. For hydrogen in water, 1 ppm = 1 mg of H2 per liter. |
| mM | Millimolar, a chemist's unit of concentration. 0.8 mM of H2 is about 1.6 ppm [3]. |
| Saturation | The most gas water can hold at a given pressure and temperature. For H2 at normal pressure and room temperature, that's about 1.6 ppm [2][13]. |
| Electrolysis | Using an electric current to split water into hydrogen gas and oxygen gas [7]. |
| ORP | Oxidation-reduction potential, a voltage reading. pH strongly affects it, so it can't tell you how much hydrogen is in water [8]. |
| Outgassing | Dissolved gas leaving the water. This is why hydrogen water loses strength after opening. |
How is hydrogen water made?
There are four common ways to get hydrogen into drinking water, plus a separate route: breathing the gas.
| Method | How it works | Worth knowing |
|---|---|---|
| Electrolysis (portable bottles, countertop generators) | An electric current splits water. Hydrogen gas forms at one electrode (the cathode) and oxygen at the other (the anode) [7]. | Some portable devices use a proton-exchange membrane (PEM) [8]. If the water contains chloride, chlorine compounds can form at the anode [8]. Output varies by device and by source water. |
| Magnesium tablets or sticks | Magnesium metal reacts with water: Mg + 2H2O → Mg(OH)2 + H2 [9]. | The reaction leaves magnesium in the water and raises the pH slightly. One study measured pH 7.9–8.1 [9]. |
| Ready-to-drink pouches or cans | Hydrogen is dissolved into water under pressure, and the water is sealed [2][8]. | Aluminum packaging holds hydrogen far better than glass or plastic [2]. |
| Water ionizers ("alkaline ionized water") | Electrolysis with a membrane. The alkaline, hydrogen-containing water from the cathode side is what you drink [7]. | Hydrogen content varies and may be well below the levels used in studies. Reviewers advise against drinking it above pH 9.8, and people with impaired kidney function should use it only under medical supervision [8]. |
| Hydrogen gas inhalation (not water) | Breathing hydrogen mixed into air or oxygen. | This is a different delivery route. Many animal studies used 1–4% hydrogen [5], and human trials have used mixtures from about 2% up to 66% hydrogen [10]. |
A note on magnesium. Each hydrogen molecule released uses up one magnesium atom. Making enough gas to saturate a liter (0.8 mmol) therefore uses about 19 mg of magnesium, and more if some gas bubbles away [2][9]. If you've been told to limit magnesium, check the label. Our kidney article covers related questions.
How to make hydrogen water at home. The practical home options are an electrolysis bottle or generator, or magnesium tablets dropped into water. Keep the container closed and drink the water promptly [2]. If you want to know the real concentration, use a method that measures hydrogen directly, such as redox-titration reagent drops or lab gas analysis, rather than an ORP meter [8]. Don't improvise with compressed hydrogen gas. Hydrogen dissolved in water isn't a fire risk [7], but hydrogen gas mixed with air or oxygen becomes explosive above about 4% [2][10].
Why do scientists study molecular hydrogen?
A 2007 study challenged the long-held view that H2 does nothing in the body [4]. In Nature Medicine, Ohsawa and colleagues reported that hydrogen reduced hydroxyl radicals, the most damaging of the "reactive oxygen species," in cultured cells. It left alone other oxygen species that cells use as signals. In a rat model of stroke, inhaling hydrogen gas reduced brain injury [1]. The authors proposed that hydrogen works as a selective antioxidant (our summary).
That paper sparked most of the research that followed [5]. Of the papers in our database with a known publication year, 2,212 of 2,291 appeared in 2007 or later [15]. Later reviews proposed further explanations: hydrogen appears to change gene activity and cell-signaling pathways, and it has shown anti-inflammatory effects in animal models [4][5].
The mechanism is still debated.
- A team of chemists pointed out that hydrogen's reaction with hydroxyl radicals, measured in earlier experiments, is too slow to matter in the body. In their own tests, H2 did not react with peroxynitrous acid, another oxidant it was proposed to neutralize [6].
- Hydrogen reacts with these radicals roughly 100 to 1,000 times more slowly than many other molecules do. Supporters argue that hydrogen spreads through tissues so quickly that this could be offset [3].
- Two puzzles remain. The reported effects don't clearly increase with dose. And gut bacteria already produce large amounts of hydrogen, yet small added amounts are reported to have effects [3].
- A review of 321 original studies concluded that radical scavenging alone can't explain the reported effects, and that the underlying "master regulator(s)" are still unknown [5].
The bottom line: there are plausible ideas about how hydrogen works, but no settled mechanism.
How much research exists?
As of September 2026, the Hydrogen Studies database contains 2,292 papers on molecular hydrogen [15]. Most of them are not studies in people:
| Type of paper | Count | Share |
|---|---|---|
| Animal studies (mostly rats and mice) | 1,113 | 49% |
| Reviews, commentaries and other papers | 505 | 22% |
| Studies in people | 391 | 17% |
| Cell and lab studies | 283 | 12% |
| Total | 2,292 | 100% |
About 600 of these papers are labeled as studies of drinking hydrogen water, and about 170 of those involved people. Other papers used inhaled gas, hydrogen-rich saline or other routes, or (like reviews) no single route [15]. These categories come from our database's labels, which can be imperfect, so treat them as approximate. See our methodology for how studies enter the database, or browse all studies. A 2023 review counted 81 registered clinical trials and 64 published human studies across all delivery methods [10].
What does the evidence say so far?
Interesting, but not conclusive. Human trials of hydrogen water are mostly small and short, and they used different products and concentrations. Many measured lab markers, such as cholesterol or oxidative-stress markers, rather than health outcomes [9][11]. Pooled analyses find small effects where they find any [11][12]. A 2026 meta-analysis of 13 randomized trials in 757 adults with overweight or obesity found total cholesterol about 6.7 mg/dL lower and LDL about 3.2 mg/dL lower with hydrogen-rich water. Triglycerides didn't change, and HDL fell slightly. The authors said these effects are below the level considered meaningful for cardiovascular risk [11]. A 2023 meta-analysis of hydrogen supplementation in 19 exercise studies (402 healthy adults) found small reductions in perceived effort and blood lactate, but no improvement in aerobic capacity or endurance performance [12]. Our full verdict is in is hydrogen water real or fake?; safety is covered in hydrogen water side effects, trial amounts in how much hydrogen water per day, and research by topic in our molecular hydrogen benefits overview.
What the evidence doesn't show
- It doesn't show that hydrogen water treats or prevents any disease. Findings in cells and animals are reasons to study it, not proof of benefit in people.
- Most of the research isn't in humans. About 6 in 10 papers in our database are animal, cell or lab studies [15]. In rodent studies, hydrogen water is usually given freely to drink [5], which is hard to compare with a person's daily intake.
- The right dose is unknown. A liter of saturated water delivers only about 0.8 mmol (1.6 mg) of hydrogen [3]. Studies used different concentrations, and some didn't measure the hydrogen content at all [7].
- The mechanism is unresolved [3][5][6].
- The number on the label isn't what's in your glass. Concentration falls after opening [2], and ORP readings can't measure hydrogen [8].
- Our counts measure volume, not quality. 2,292 papers doesn't mean 2,292 positive results. Many are reviews, and many animal studies test conditions that don't match everyday drinking.
Frequently asked questions
Is molecular hydrogen the same thing as hydrogen water?
Not quite. Molecular hydrogen (H2) is the gas itself, and hydrogen water is one way to take it in. Researchers have also studied inhaling the gas, hydrogen-rich saline injections, hydrogen baths and eye drops. Results from one route don't automatically apply to another.
Is hydrogen water the same as alkaline or ionized water?
No. Alkaline water is defined by a high pH, while hydrogen water is defined by dissolved H2 gas. Water ionizers make alkaline water that can contain some hydrogen, but the amount varies and may be well below the levels used in studies. Reviewers also advise against drinking ionizer water above pH 9.8.
How long does hydrogen stay in water?
It starts escaping once the container is open, and it also passes through plastic and glass. Sealed aluminum pouches and cans hold it much longer. Drink hydrogen water soon after making or opening it.
Can you make hydrogen water at home?
Yes. The usual home methods are an electrolysis bottle or countertop generator, or magnesium tablets that react with water to release hydrogen. Keep the container closed, drink it promptly, and if you want to know the concentration, use hydrogen-specific test reagents rather than an ORP meter. Don't improvise with compressed hydrogen gas, which is a fire and explosion hazard.
Is hydrogen water FDA approved?
Not as a treatment for anything. In 2014 the FDA said it had no questions about a company's conclusion that hydrogen gas is generally recognized as safe (GRAS) as an ingredient in drinking water and other beverages. That response is about safety as a food ingredient, not about any health benefit.
Sources
- Ohsawa I, et al. Hydrogen acts as a therapeutic antioxidant by selectively reducing cytotoxic oxygen radicals. Nature Medicine. 2007. PubMed · Our summary
- Ohta S. Recent progress toward hydrogen medicine: potential of molecular hydrogen for preventive and therapeutic applications. Current Pharmaceutical Design. 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
- Ohta S. Molecular hydrogen as a preventive and therapeutic medical gas: initiation, development and potential of hydrogen medicine. Pharmacology & Therapeutics. 2014. PubMed · Our summary
- Ichihara M, et al. Beneficial biological effects and the underlying mechanisms of molecular hydrogen: comprehensive review of 321 original articles. Medical Gas Research. 2015. PubMed · Our summary
- Penders J, et al. ONOOH does not react with H2: potential beneficial effects of H2 as an antioxidant by selective reaction with hydroxyl radicals and peroxynitrite. Free Radical Biology & Medicine. 2014. PubMed · Our summary
- LeBaron TW, et al. Electrolyzed-reduced water: Review I. Molecular hydrogen is the exclusive agent responsible for the therapeutic effects. International Journal of Molecular Sciences. 2022. 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
- Nakao A, et al. Effectiveness of hydrogen rich water on antioxidant status of subjects with potential metabolic syndrome: an open label pilot study. Journal of Clinical Biochemistry and Nutrition. 2010. PubMed · Our summary
- Johnsen HM, et al. Molecular hydrogen therapy: a review on clinical studies and outcomes. Molecules. 2023. PubMed · Our summary
- Ye H, et al. The effect of hydrogen-rich water interventions on lipid profiles in adults with overweight or obesity and associated metabolic disorders: a systematic review and meta-analysis of randomized controlled trials. Diabetology & Metabolic Syndrome. 2026. PubMed · Our summary
- Zhou K, et al. Effects of molecular hydrogen supplementation on fatigue and aerobic capacity in healthy adults: a systematic review and meta-analysis. Frontiers in Nutrition. 2023. PubMed · Our summary
- National Institute of Standards and Technology. NIST Chemistry WebBook, SRD 69: Henry's law data for hydrogen (k°H ≈ 0.00078 mol/(kg·bar) at 25 °C) and carbon dioxide (k°H ≈ 0.034 mol/(kg·bar) at 25 °C).
- U.S. Food and Drug Administration. GRAS Notice No. 520: Hydrogen gas (FDA response "no questions," November 28, 2014). FDA GRAS Notices inventory
- Hydrogen Studies database. Counts by study type, delivery method and publication year, queried September 23, 2026. Browse the studies
Conflicts of interest in these sources: sources 7 and 8 were written by authors affiliated with the Molecular Hydrogen Institute, a nonprofit that promotes hydrogen research, and H2 Analytics, a hydrogen-testing company that has certified products for Echo Technologies, which funds this site. Two authors of source 10 are named inventors on hydrogen-release patent applications assigned to Nacamed AS, a company one of them is affiliated with. We cite these sources for their chemistry and study counts, not their conclusions about benefits.
How we wrote this: 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 — talk to your clinician before changing any treatment.