Upon nearly every single altar, you will find two small bowls. The bowls themselves can be of any size shape or color, their appearance is not the point here. What is important however is their contents.
In the first bowl is usually found a small amount of the sacred salt. Salt is generally used for casting the circle, consecration of tools, and many other purposes. Rock salt symbolizes Earth, and is mixed with water and sprinkled over things to purify them. Sea Salt symbolizes water and earth, and is more commonly used.

In the second bowl is usually found a small amount of water. The water is for cleansing, and is used during rites and rituals to cleanse the tools and area.

Used in conjunction, this is a powerful way to cleanse, purify, and bless ritual tools and to cast the circle.