Where does “hydato-” come from?

hydato- (English) comes from Ancient Greek ὕδωρ, from Proto-Hellenic *údōr.

Ancestry of “hydato-”, step by step

Step	Language	Word	Meaning
1	Ancient Greek	ὕδωρ	water; rainwater, rain; sweat
2	Proto-Hellenic	*údōr	—

hydato- — Etymology, Origin & Word History | Etymology Explorer