It is a colorless crystal or white powder and is produced when quicklime (calcium oxide) is mixed, or slaked with water. It has many names including Calcium Hydroxide, caustic lime, builders' lime, slack lime, cal, or pickling lime, and is relatively insoluble in water.
One significant application of calcium hydroxide is as a flocculant, in water and sewage treatment. It forms a fluffy charged solid that aids in the removal of smaller particles from water, resulting in a clearer product.
This application is enabled by the low cost and low toxicity of calcium hydroxide. It is also used in fresh water treatment for raising the pH of the water so that pipes will not corrode where the base water is acidic, because it is self-regulating and does not raise too much the pH
Another large application is in the paper industry, where it is an intermediate in the reaction in the production of sodium hydroxide.