Old English wæter, from Proto-Germanic *watr- (source also of Old Saxon watar, Old Frisian wetir, Dutch water, Old High German wazzar, German Wasser, Old Norse vatn, Gothic wato "water"), from PIE *wod-or, suffixed form of root *wed- (1) "water; wet." In ancient conceptions one of the handful of basic elements of which everything is composed.
To have one's head above water (and thus avoid drowning) is by 1660s; in the figurative sense "out of difficulty" it is recorded from 1742.
Water-cure for healing therapies involving water is by 1842. The crowd-control water-cannon is so called by 1964; water-fountain "drinking fountain" is by 1946. Water-buffalo is attested by 1894. Water polo is attested from 1884; water torture from 1928.
Waters for "seas of a particular region," especially "maritime claims of a nation," is by 1650s.
Linguists believe PIE had two root words for water: *ap- and *wed-. The first (preserved in Sanskrit apah as well as Punjab and julep) was "animate," referring to water as a living force; the latter referred to it as an inanimate substance. The same probably was true of fire (n.).
