How We Test
What each judgement is based on, where every number comes from, and where we say we don't know.
Every ranking on this site comes from The H2 Index, a six-factor score weighted toward verified dissolved-hydrogen output and generation technology. Commission rates are not an input. Where a manufacturer publishes no figure, we print “not published” rather than repeating a range from a sales page.
The six factors
| Factor | Weight | What it covers |
|---|---|---|
| Published H2 output | 28% | Dissolved hydrogen in mg/L (ppm). A figure backed by an independent lab certificate scores above a manufacturer figure, which scores above a marketing range. We do not measure output ourselves and never score a machine as though we had. |
| Generation technology | 18% | SPE/PEM membrane separation versus open electrolysis plates, and whether ozone and chlorine byproducts are vented. |
| Capacity and cycle time | 17% | Litres per cycle and minutes per cycle, scored against household demand. |
| Warranty and support | 12% | Warranty length, parts availability, and filter or plate replacement cost. |
| Three-year cost per litre | 20% | Purchase price plus consumables and electricity, divided by realistic household output. Weighted above warranty because price is the factor most buyers actually decide on. |
| Hydrogen inhalation | 5% | Whether the unit also delivers hydrogen gas for inhalation. A genuine capability difference rather than a spec tier, so it carries a small weight - enough to separate two otherwise equal machines, not enough to carry a bad one. |
The Index is not scored in the abstract. It is applied on every ranking page - the best hydrogen water generators, the portable hydrogen water generators and the hydrogen inhalation machines - and every factor is shown per machine in the side-by-side comparison rather than rolled up into one number.
What we do and do not do
We own two of the products we rank - the Lourdes Hydrofix and the Echo Flask - and the photographs of those are ours. We do not own the rest, and every page says so in a box headed “what this assessment is based on”, because a reader deserves to know whether a judgement came from using a machine or from reading its spec sheet. What we also do not do is measure dissolved hydrogen. That needs a calibrated meter, a repeatable protocol and a published margin of error, and any site claiming it without all three is guessing. If you want to see what the measurement actually involves, Seo and colleagues set out the titration method that the consumer reagent drops are based on.
So every concentration figure on this site is attributed. An independent lab certificate outranks a manufacturer figure, which outranks a marketing range, and the label next to each number tells you which one you are reading. Across the whole catalogue exactly one product - the Echo Flask - has a third-party certificate behind its output claim. That is not a gap in our research; it is the state of the category.
There is no independent testing body for hydrogen water generators. Consumer Reports does not rate them. Treating a manufacturer range as though it were a measured result is the single most common failure in this niche, and refusing to do it is the whole point of this site. What we can tell you first-hand is what these machines are like to own: how long a cycle really takes, how the build holds up, what the support is like, and whether the thing ends up on the counter or in a cupboard.
We also will not publish a review with no drawbacks. Every product on this site carries at least two genuine criticisms, and a review page that cannot meet that bar stays in draft until it can.
The science this rests on
Five papers do most of the work behind the judgements on this site. None of them is about what hydrogen does in a body - that question is outside what this site covers. They are about water chemistry and electrolysis hardware, which is what we rank.
Two are worth knowing before you spend anything. Hydrogen is only sparingly soluble in water, and the standard solubility compilation puts the practical ceiling near 1.6 mg/L at room temperature and ordinary pressure - so a machine advertising several times that figure is either using unusual conditions or is not describing what ends up in your glass. And the negative ORP reading printed on so many boxes is not a hydrogen measurement at all: LeBaron and Sharpe show that pH and temperature shift that number far more than dissolved hydrogen does.
The other three explain why we treat generation technology as a scoring factor rather than a spec-sheet word. Carmo and colleagues describe what a proton-exchange membrane is doing, and Bergmann and colleagues show that passing a current through drinking water can form byproducts from whatever is dissolved in it, at rates that depend heavily on electrode material and operating conditions. That is the argument for keeping electrolysis in a chamber separate from the water you drink - not a claim about any particular machine on this site.
- 01
Sander, R. (2023). Compilation of Henry's law constants (version 5.0.0) for water as solvent. Atmospheric Chemistry and Physics 23, 10901-12440. Free to read.
The solubility ceiling. Hydrogen gas is only sparingly soluble in water, which is why dissolved-hydrogen figures cluster near 1.6 mg/L at room temperature and normal pressure, and why a claim far above that needs an explanation attached.
- 02
LeBaron, T. W. and Sharpe, R. (2022). ORP should not be used to estimate or compare concentrations of aqueous H2: an in silico analysis and narrative synopsis. Frontiers in Food Science and Technology 2, 1007001. Free to read.
Why we ignore ORP. A negative oxidation-reduction potential reading is the most common thing marketing puts on the box, and it does not tell you the hydrogen concentration: pH and temperature move the number far more than hydrogen does.
- 03
Seo, T., Kurokawa, R. and Sato, B. (2012). A convenient method for determining the concentration of hydrogen in water: use of methylene blue with colloidal platinum. Medical Gas Research 2, 1. Free to read.
What an actual dissolved-hydrogen measurement involves. This is the titration method behind the reagent drops sold to consumers, and reading it is the quickest way to see why we do not claim to measure output ourselves.
- 04
Carmo, M., Fritz, D. L., Mergel, J. and Stolten, D. (2013). A comprehensive review on PEM water electrolysis. International Journal of Hydrogen Energy 38, 4901-4934. Paywalled.
What SPE/PEM actually means. The proton-exchange membrane every brand puts on its spec sheet is standard industrial electrolysis, described here in full, and knowing that makes it easier to tell a real design claim from a rebranded one.
- 05
Bergmann, H., Iourtchouk, T. and Hartmann, J. (2015). Laboratory- and technical-scale comparison of chlorate and perchlorate formation during drinking water electrolysis: a field study. Journal of Applied Electrochemistry 45, 765-778. Paywalled.
Why the electrode and the chamber design matter. Running a current through drinking water can form byproducts from whatever is dissolved in it, at rates that depend heavily on electrode material and operating conditions - which is the case for keeping electrolysis separate from the water you drink.
How we make money
Affiliate commissions, disclosed on every page that carries a link. Some of the products we rank pay us nothing, including one currently in our top three. Rankings are set before programs are applied for, and no brand has ever been shown a review before publication.
Corrections
Prices are rechecked monthly and every page carries its last-updated date. If a specification here is wrong, tell us and we will fix it and note the change - the contact page is the fastest route.