This guide covers both formats — dissolved concentration in water, and inhaled gas concentration — since the same measurement-point problem shows up in both, just differently.
Part 1: Dissolved hydrogen in water (ppm / ppb / mg/L)
The physical ceiling. At 1 atmosphere and room temperature, water can only hold about 1.6 mg/L (1.6 ppm) of dissolved H₂ before it reaches saturation — a hard Henry's Law limit, not a design choice. Anything claimed above that figure is achieved through pressurized or sealed-vessel generation (supersaturation), which is real physics, not a red flag on its own.
The part that's usually missing: when was it measured? Dissolved hydrogen starts escaping the moment water is exposed to open air — it's the smallest, most diffusive molecule there is. Published dissipation data puts the half-life of dissolved H₂ in an open 500 mL container at roughly two hours at room temperature, faster with any agitation. A tablet, bottle, or machine that states a ppm figure without saying whether it was measured at the moment of production or several minutes later is giving you the more flattering number, not the more useful one.
What to actually ask a brand, or check for on their spec sheet:
- Was this measured at the point of production, or after a stated delay?
- Was it tested in a sealed container or open glass?
- Is there a third-party lab certificate, and does it specify the measurement protocol?
A concentration is not the same as a dose. The amount of H₂ you actually consume depends on concentration and volume. A 500 mL glass at 1.6 ppm delivers about 0.8 mg of H₂; the same concentration in 250 mL delivers half that. A brand's headline ppm number tells you nothing about total dose without knowing how much you're drinking. For the wider context on how machines produce dissolved hydrogen in the first place, see our primer on what a hydrogen water machine is and how it works, and the format comparison in hydrogen tablets vs. machines.
Part 2: Inhaled hydrogen concentration (FiH₂%)
Inhalation measures concentration differently — as a percentage of the gas mixture you're breathing (FiH₂), not a dissolved amount in liquid. This sidesteps the water-dissolution decay problem entirely, since you're breathing the gas directly rather than drinking water that's already started losing hydrogen. But it introduces its own things worth checking.
The published safety and research range. Most published inhalation studies use concentrations in the 1–4% FiH₂ range, for sessions typically between 15–60 minutes. This is also a hard safety boundary, not just a research convention: hydrogen-air mixtures above roughly 4% become potentially flammable. A well-engineered inhaler should be specifically designed to keep output within this range reliably, not just capable of high output in principle.
Flow rate and concentration are related but not identical. A device's flow rate (measured in mL/min) tells you how much gas it produces per minute. That's a genuine, checkable, third-party-verifiable spec. But flow rate alone doesn't tell you the FiH₂% actually reaching your lungs — that depends on the delivery method (sealed mask vs. open nasal cannula), any dilution from ambient air, and whether the gas stream is pure H₂ or a combined H₂/O₂ mixture.
What to check on any inhaler's spec sheet:
- Stated purity (% of the gas stream that's actually H₂, not diluted or contaminated)
- Whether output is separated pure hydrogen or a combined gas stream
- Consistency of flow rate over a full session, not just a peak figure
- Whether the FiH₂% delivered to the user has been independently tested, or only the machine's raw gas production
For a worked example of how these figures compare between two real inhalers at the same flow-rate tier, see our decision-aid comparison QY-A1800 vs. Echo Refresh: which hydrogen inhaler should you buy?
Part 3: Why cross-checking multiple sources on the same product matters
Across every brand we've reviewed in building this site's comparison content, the same pattern shows up: a single product often has different concentration or flow-rate figures listed across its own manufacturer page, reseller listings, and third-party test sites. This isn't necessarily deception — testing conditions vary, and older figures don't always get updated everywhere a product is sold — but it means a single number from a single listing shouldn't be treated as definitive. Where possible, check the manufacturer's own spec sheet, an independent lab certificate if one exists, and at least one third-party test, and expect some variance between them.
The honest summary
Neither "our tablets do 10 ppm" nor "our machine only does 1.5 ppm" is inherently false — they're often measuring different things (peak-at-production vs. equilibrium, or gross flow rate vs. delivered concentration). The number that matters isn't the biggest one on the label — it's the one that specifies exactly when, how, and under what conditions it was measured. Any brand willing to state that clearly is giving you something to actually evaluate; any brand that only gives you the headline number is asking you to trust it on faith.
This guide applies the same evidentiary standard to every product we discuss, including our own. Where we cite a concentration or purity figure for our own machines, it should carry the same measurement-point disclosure this guide asks of everyone else — flag it if it doesn't.