How Much Hydrogen Can Water Actually Hold? Reading the PPB Figure on a Hydrogen Bottle

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Before the question of whether hydrogen water does anything, there is a smaller question that can actually be settled: can water hold the amount these bottles say they put in it. For the generator in our own catalogue the answer is that its headline figure is roughly three times the concentration water holds at equilibrium under a full atmosphere of pure hydrogen. That does not make the number a lie. It does tell you what kind of number it is, and the arithmetic takes two lines.

Convert the figure first, because ppb hides the scale

Concentrations in parts per billion are easy to quote and hard to feel. In water, one part per billion is one microgram per litre, so the conversion is just decimal places.

The bottle in our catalogue is described by its maker as reaching up to 4,780 ppb of dissolved molecular hydrogen. That is 4,780 micrograms per litre, which is 4.78 milligrams per litre. Hold on to 4.78, because the only other number you need is the one it has to be compared with.

The ceiling comes from Henry's law, and it is low

How much of a gas dissolves in a liquid is governed by Henry's law: at a given temperature, the concentration that dissolves is proportional to the partial pressure of that gas sitting above the liquid. Double the pressure of the gas and you double the dissolved amount. Take the gas away and the dissolved amount goes with it.

Hydrogen is a poorly soluble gas. As a rule of thumb from standard solubility data rather than anything we measured, water at about 25 degrees Celsius with one atmosphere of pure hydrogen above it holds roughly 1.6 milligrams per litre at equilibrium, a figure often quoted as 1.57. In the units on the box that is about 1,600 ppb. And note the condition attached to it, because it is a strong one: one full atmosphere of pure hydrogen, not air.

So the division is 4.78 divided by 1.6, which is almost exactly 3. The stated figure sits about three times above the equilibrium ceiling. Put the other way round, to hold 4.78 milligrams per litre as a resting concentration you would need something like three atmospheres of pure hydrogen pressing on the water, in the region of 44 psi, which is not what a rechargeable plastic drinking bottle does.

Why that is not the same as calling the number false

Here is the part that keeps this honest, because supersaturation is a real and completely ordinary state. A sealed can of fizzy drink is carrying far more dissolved carbon dioxide than water holds at atmospheric pressure, which is exactly why it fizzes when you break the seal: it was above its ceiling, and opening it let it fall back. Electrolysis can do something similar on a small scale, generating hydrogen right at the electrode surface and pushing the water next to it above equilibrium for a while.

So a reading of 4,780 ppb taken at the right moment, in the right place, may well be a genuine measurement. What it cannot be is a steady state. A figure above the ceiling is by definition a figure that is on its way down, and the useful question is not how high the peak was but what the concentration is when the water reaches you.

That is where this gets worse rather than better, and the reason is the second half of Henry's law. The atmosphere is not pure hydrogen. It contains hydrogen at something under one part per million by volume, so the hydrogen partial pressure above an open glass is close to zero, and the equilibrium concentration it implies is a millionth or so of the 1.6 figure. In other words there is no plateau at the dashed line in the diagram for the water to settle onto. Left open, it does not decay to saturation and stop. It decays towards empty. Sealing the bottle, keeping it cold, leaving no headspace and not shaking it all slow that down, and as a rule of thumb nothing stops it.

Which means the specification that would actually matter is one no listing publishes: the concentration some stated number of minutes after the cycle ends, and how it was measured. The peak is the easiest figure to generate and the least informative one to own.

What the bottle in our catalogue publishes

An 8 oz hydrogen water bottle generator is the device the numbers above come from, and its record is better than most at labelling its own claims. It lists SPE and PEM electrolysis with a dual chamber design, a BPA free PCTG body, one-touch operation, a rechargeable 8 oz capacity, and up to 4,780 ppb explicitly marked as maker stated, with the listing attributing it to hydrogen-specific testing. Our own record is equally explicit that the concentration figure is maker stated rather than lab verified by us, and we have not measured it either.

Two more things on that record deserve reading alongside the arithmetic. The first is the capacity, because 8 fluid ounces is about 237 millilitres, so even at the full stated 4.78 milligrams per litre a whole bottle contains in the region of 1.1 milligrams of hydrogen, and at the equilibrium ceiling it would be about 0.38 milligrams. Whatever you believe dissolved hydrogen does, these are the quantities involved. The second is the limit the record states plainly: it infuses hydrogen and does not filter or purify anything, so it needs clean drinkable water going in, and the power adapter details are not specified in the listing. Details in our review of the 8 oz hydrogen generator, and the broader checklist is in how to choose a hydrogen water bottle.

Whether any of this is worth drinking is a question about human physiology that this page is not equipped to settle, and we are not going to pretend otherwise. We make no health claim for hydrogen water in either direction. What the arithmetic does give you is a way to read a competing listing: convert the ppb figure to milligrams per litre, divide by 1.6, and you know immediately whether you are being quoted a resting concentration or a peak.

The part that actually affects you daily

One unglamorous note, because it applies to any bottle you refill every day and has nothing to do with hydrogen. An electrolysis bottle has a chamber, a lid and sealing rings that stay permanently damp, and that geometry is where biofilm grows in every reusable bottle. A cup lid and bottle cleaning brush set exists for exactly those surfaces: its record lists three brushes, each pairing two rows of stiff bristles with a slender soft tip for narrow bottle holes and a built-in pry bar for lifting sealing rings, in PP plastic, with a 180 degree rotatable head and a hanging hole for drying. The record is candid that no dimensions or bristle length are published and that these are detail tools rather than anything for large surfaces. See our review of the brush set, and the method is in how to clean cup lids, bottle spouts and rubber seals. A seal you cannot reach will affect what you drink more reliably than a few hundred ppb either way.

The honest limit

The limit here is unusually clean, because it is set by physics rather than by engineering. No bottle, at any price, with any electrode, holds water much above about 1.6 milligrams per litre of hydrogen once it has had a chance to come to equilibrium with the air in the room, and every open container is losing hydrogen continuously towards a level near zero. A better machine can reach a higher peak and reach it faster. It cannot change where the water ends up, and it cannot stop the clock that starts the moment you unscrew the lid.

So if you are comparing bottles on their ppb figures, you are comparing peaks, which is the one specification the physics makes least durable. And if what you actually wanted was to drink more water, which is the honest answer for a lot of people asking about these, then a bottle you like carrying and remember to refill does that job completely, and the electrolysis is beside the point.