Water was one of the western classical elements the other being earth air and fire symbols.
According to Kurt Seligmann's The History of Magic and the Occult (1948), the year was traditionally divided in two by the ancient people: spring-summer was the male season of the sun, warmth and dryness while autumn-winter was the female season of the moon, coolness and moisture because it was the wet season for most of the world.
Water was connected to the moon scientifically, as well, as the moon's gravitational pull affects tidal flow.
In Isaac Newton's translation of the Hermetic Emerald Tablet, he rendered the elements as Sun (fire), Moon (water), Wind (air) and Earth - the four elements 'above and below' that came together for the one thing (Life).
In the Tao Te Ching, we were told to 'know the masculine but keep to the feminine.' Bruce Lee quoted an ancient Oriental proverb when he said "Be water my friend, be water," which was to say be flexible, adaptable in mind and body.
Its cleansing properties meant that it was seen as a means of purification, whether in the form of individual baptism or global deluge (e.g. Noah's or Deucalion's Flood, Manu's, etc.), both of which were universal ideas. Similarly, its opposite (fire) was considered equally 'cleansing' as can be seen in The Book of Revelation.
For this reason, it was also considered by the alchemists to be a "universal solvent", a notion modern science echoed precisely. There were two forms of alchemical water, said Socrates, but both were described as 'fire' and 'water' in a single substance. (See: C.G. Jung, Psychology and Alchemy).
There was a very old parable, ultimately of Oriental origin but it appeared in the Book of Matthew, which described Enlightenment as the crossing of a river.