Definition
Dissolving hydrogen does not change the water's pH in any meaningful way and does not require ionisation. The two ideas are frequently conflated in marketing.
Because hydrogen is poorly soluble and escapes readily, concentration at the moment of drinking matters more than the figure printed on a machine.
Modality relevance
Hydrogen-rich water is the third consumer format alongside inhalation and bathing, and is generally the lowest-friction entry point.
Purity relevance
Water-format machines still depend on cell design and materials in the wetted path; purity language again describes hardware.
Science relevance
Drinking-water studies are among the more common designs in the literature, and carry the same exploratory caveats.