Figure 2: Relationship between types of water and dissolved hydrogen concentration (DH). Note: (A) Hydrogen was scarcely generated in the purified water. Hydrogen concentration before hydrogen-water production was below the detection sensitivity limit of 10 μg/L. (B) As the hardness of mineral water increased, the post-electrolytic DH tended to decrease. At the time of hydrogen-water production, a water amount was 300 mL, and a water temperature was 20°C, with a hydrogen-water generator using direct current electrolysis method.