Water can be identified by the use of anhydrous copper (II) tetraoxosulphate (VI). Anhydrous copper (II) tetraoxosulphate (VI) is a white crystalline solid that readily absorbs water from the atmosphere to form copper (II) tetraoxosulphate (VI) pentahydrate, which is blue in colour. When anhydrous copper (II) tetraoxosulphate (VI) is added to water, it turns blue as the water molecules hydrate the copper (II) ions to form the blue pentahydrate. This reaction is used as a simple and quick test for the presence of water.