What is actually in the glass
Hydrogen-rich water is water with H₂ gas dissolved in it. The molecule is not bonded to the water and does not change the water's composition; it is simply present in solution, in the same way carbon dioxide is present in sparkling water.
That framing answers most beginner questions at once. There is no residue, no taste, no additive and nothing to accumulate — and equally, nothing that stays put once the gas has a route to the atmosphere.
How it is produced
A PEM/SPE cell splits water into hydrogen and oxygen and feeds the hydrogen into the drinking-water side. Because the membrane separates the two gases, the oxygen and any by-products can be vented rather than dissolved.
This is the technical reason to care about cell type in a water generator: an undifferentiated mixed-gas cell puts everything it makes into the same stream.
Why concentration fades
Dissolved hydrogen leaves solution fast. Pour it, stir it, or leave the lid off, and concentration drops within minutes. Warm water holds less than cold, and agitation accelerates loss.
Practically, this means the honest way to use hydrogen water is to make it and drink it, not to make it and store it. Any bottled product claiming a shelf-stable dissolved-hydrogen figure deserves scepticism about how and when that figure was measured.
Hydrogen water is not alkaline water
Alkaline and ionised water marketing concerns pH — how acidic or basic the water is. Dissolved hydrogen concentration is a different variable entirely, and a high pH tells you nothing about H₂ content.
The two get conflated because some ionisers incidentally produce hydrogen. If dissolved hydrogen is the thing you care about, measure or specify dissolved hydrogen.
Where source water quality comes in
Whatever is in the source water is still in the glass afterwards; electrolysis adds hydrogen, it does not purify. That is why RO filtration and hydrogen generation are often paired in one appliance.
As always: general wellness context only. We make no health-outcome claims for hydrogen water.