water

water one of the four elements in ancient and medieval philosophy and in astrology (considered essential to the nature of the signs Cancer, Scorpio, and Pisces).

The word is recorded from Old English (in form wæter) and is of Germanic origin; it comes from an Indo-European root shared by Lain unda ‘wave’ and Greek hudōr ‘water’.
don't go near the water until you learn how to swim proverbial saying, mid 19th century; advising against overconfidence when inexperienced.
of the first water referring to the highest grade of diamond. The three highest grades of diamond were formerly known as first, second, and third water, and the phrase of the first water is used generally to indicate the finest possible quaility. The usage may come ultimately from Arabic, where this sense of water is a particular application of ‘lustre, splendour’ (e.g., of a sword).
Water Bearer the zodiacal sign or constellation Aquarius, also called the Water Carrier.
water under the bridge referring to events or situations that are in the past and consequently no longer to be regarded as important or as a source of concern (in North American usage, water over the dam).

See also blood is thicker than water, bread and water, clear blue water, dead in the water, dirty water will quench fire, fish out of water, fish in troubled waters, come hell or high water, you can take a horse to water, still waters run deep, don't throw out your dirty water.