Hydrogen water is simply water that has had H2 (hydrogen gas) dissolved into it. The end products yields a gas-dissolved solution, similar to carbonation which adds CO2 (carbon dioxide) to water to make sparkling water. The difference being hydrogen gas is added instead of carbon dioxide.
What is Hydrogen Gas?
Hydrogen gas is simply two hydrogen atoms bound together to form molecular hydrogen or H2. It is a colourless, odorless neutral gas that is non-polar and largely non-reactive.
Wait... Isn't Hydrogen Gas EXPLOSIVE? Like the Hindenburg?
Molecular hydrogen is only explosive above 4.6% of the atmospheric pressure. The hydrogen tables do not produce enough gas to breach this threshold in any reasonable measurement. Further, when dissolved in water, it is neither explosive not flammable. There is no risk from the hydrogen tablets or from hydrogen water.
Isn't ALL Water Hydrogen Water?
While water does contain two parts hydrogen and one-part oxygen, regular water (H2O) is not the same as hydrogen water. In H2O, the molecules are bound together, whereas hydrogen water is a "solution", where the H2 gas is dissolved into the H2O.
...But, Isn't Water Still Two Parts Hydrogen? So, Can't I Just Drink More Water?
If the goal is to obtain therapeutic hydrogen gas, then drinking more water will not accomplish this goal, no matter how much you drink. Changing a compound, changes its properties. The components of a compound do not necessarily possess the same characteristics as the compound. Likewise, a compound doesn't necessarily have similar characteristics as its components.
A good example is sodium chloride (NaCl). Sodium in its elemental form is highly explosive, and very dangerous. By dropping sodium metal into water, it will violently explode, potentially shattering the container and igniting in flames fueled by an exothermic reaction and the release of hydrogen gas. Chlorine is a toxic gas. Bound together as NaCl, they become table salt, which is water soluble (and doesn't explode or make H2O) and delivers ionic elemental sodium, which we need in certain quantities to maintain biological function. Of course, too much sodium comes with negative health consequences.
As for hydrogen water, when H2 is bound to oxygen we cannot obtain its therapeutic benefit no more than we can breathe the oxygen bound to water. Thus, we need to dissolve extra hydrogen gas into regular water to obtain hydrogen water.
Hydrogen Water is NOT Hydrogen Peroxide
Hydrogen peroxide (H2O2) is a string oxidizing agent. The only similarity between the two is that they both have a hydrogen molecule in the compound. As discussed in the previous section, even compounds with similar make ups can have dramatically different behaviours.
Hydrogen Water is NOT H3O OR H4O
Adding hydrogen gas to water does not change the water to H3O or H4O. It simply adds gas to water that dissolves into solution (or maintains itself in a quasi-dissolved state, such as in our tablets). Hydrogen water is still H2O, just with extra hydrogen gas added.
Hydrogen Water is NOT Alkaline Water
While some water ionizers market themselves as both alkaline and hydrogen water makers, adding hydrogen gas to water does not change its pH. We have a full article coming out on the misconceptions between alkkaline water and hydrogen water.
Hydrogen gas, as a neutral molecule, does not increase the pH of a solution. This is a sticky point for many, as pH is a measurement of hydrogen ions. To understand the differrences between the several forms of hydrogen, the MHI has an article here title "Dummies Guide to Hydrogen".