Late 16th century: (earlier (late Middle English) as inundation) from Latin inundat- 'flooded', from the verb inundare, from in- 'into, upon' + undare 'to flow' (from unda 'a wave').

• water from Old English:

  The people living around the Black Sea more than 5 000 years ago had a word for water. We do not know exactly what it was, but it was probably the source for the words used for ‘water’ in many European languages, past and present. In Old English it was wæter. The Greek was hudōr, the source of words like hydraulic (mid 17th century) and hydrotherapy (late 19th century). The same root led to the formation of Latin unda ‘wave’, as in inundate (late 18th century), abound (Middle English) (from Latin abundare ‘overflow’), and undulate (mid 17th century), Russian voda (the source of vodka), German Wasser, and the English words wet (Old English) and otter (Old English). Of the first water means ‘unsurpassed’. The three highest grades into which diamonds or pearls could be classified used to be called waters, but only first water, the top one, is found today, describing a completely flawless gem. An equivalent term is found in many European languages, and all are thought to come from the Arabic word for water, mā, which also meant ‘shine or splendour’, presumably from the appearance of very pure water. People and things other than gems began to be described as of the first water in the 1820s. Nowadays the phrase is rarely used as a compliment: in a letter written in 1950, P.G. Wodehouse commented disparagingly on J. M. Barrie's play The Admirable Crichton: ‘I remember being entranced with it in 1904 or whenever it was, but now it seems like a turkey of the first water.’ If you study a duck shaking its wings after diving for food you will see the point of water off a duck's back, used since the 1820s of a potentially hurtful remark that has no apparent effect. The water forms into beads and simply slides off the bird's waterproof feathers, leaving the duck dry. Water under the bridge refers to events that are in the past and should no longer to be regarded as important. Similar phrases are recorded since the beginning of the 20th century. A North American variant is water over the dam. The first uses of waterlogged, in the late 18th century, referred to ships that were so flooded with water that they became heavy and unmanageable, and no better than a log floating in the sea. A watershed, a ridge of land that separates waters flowing to different rivers or seas, has nothing to do with garden sheds but means ‘ridge of high ground’ and is connected with shed (Old English) meaning ‘discard’.