In ancient times, Water was considered one of the 4 or 5 elements of nature.  Earth Water Air, and Fire were the four classical element of greek philosophy until Aristotle added a fifth element, Aether or void. It was called the quintessence (fifth element).  Other philosophies and religions, believed all five were classic elements that made up all things.  When you died, your being would return to the five fundamental elements, re-establishing balance.
 
In Greece, Water was given the symbol of an upside down triangle, which is still used in engineering to designate water.  It is also associated with the qualities of emotion and intuition.
 
In the I Ching, the planet Mercury is associated with the Element water.  Other elements are associated with the other 4 closest planets to earth (interestingly, the planet Saturn is associated with the element Earth).  This association influenced medieval alchemists who created a symbol for the element Mercury with an upward pointing triangle with a horizontal line through the middle.


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