The ornamental design for a hydrogenwatergenerator, as shown and described.
FIG. 1 is a perspective view of a hydrogen water generator showing my new design;
FIG. 2 is a front plan view thereof;
FIG. 3 is a rear plan view thereof;
FIG. 4 is a left side plan view thereof;
FIG. 5 is a right side plan view thereof;
FIG. 6 is a top plan view thereof; and,
FIG. 7 is a bottom plan view thereof.
The broken lines shown in Figs. are included for purpose of illustrating portions of the hydrogen water generator which form no part of the claimed design.