Douglas Harper's Etymology Dictionary
aqua-
word-forming element meaning "water," from Latin aqua "water; the sea; rain," cognate with Proto-Germanic *akhwo, source of Old English ea "river," Gothic ahua "river, waters," Old Norse Ægir, name of the sea-god, Old English ieg "island;" all from PIE *akwa- "water" (cognates: Sanskrit ap "water," Hittite akwanzi "they drink," Lithuanian uppe "a river").
Wiktionary
aqua-
pre. Pertaining to water