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."
To keep (one's) head above water in the figurative sense is recorded from 1742. Water cooler is recorded from 1846; water polo from 1884; water torture from 1928. 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.).
Old English fugel "bird, feathered vertebrate," from Proto-Germanic *fuglaz, the general Germanic word for "bird" (source also of Old Saxon fugal, Old Frisian fugel, Old Norse fugl, Middle Dutch voghel, Dutch vogel, German vogel, Gothic fugls "a fowl, a bird"), perhaps a dissimilation of a word meaning literally "flyer," from PIE *pleuk-, from root *pleu- "to flow."
Displaced in its original sense by bird (n.); narrower sense of "barnyard hen or rooster" (the main modern meaning) is first recorded 1570s; in U.S. this was extended to domestic ducks and geese.