Taken from about.com:
Water is a feminine energy and highly connected with the aspects of the Goddess. Used for healing, cleansing, and purification, Water is related to the West, and associated with passion and emotion. In many spiritual paths, including Catholicism, consecrated Water can be found – holy water is just regular water with salt added to it, and usually a blessing or invocation is said above it. In Wiccan covens, such water is used to consecrate the circle and all the tools within it. As you may expect, water is associated with the color blue, and the Tarot suit of Cup cards.