Hydrate

Cobalt Chloride before and after hydration

Hydrate is a term used in inorganic chemistry and organic chemistry to indicate that a substance contains water. The chemical state of the water varies widely between hydrates.
Mineral hydrates are inorganic salts containing water molecules combined in a definite ratio as an integral part of the crystal that are either bound to a metal center or that have crystallized with the metal complex.
A colorful example is cobalt chloride, which turns from blue to magenta upon hydration, and can therefore be used as a water indicator.

@ Learn more about hydrates