When water reacts with alkali metals such as sodium, alkali are formed. The reason they are called alkali metals. Also, the colour change from white anhydrous copper(II) tetraoxosulphate(VI) to blue hydrated copper(II) tetraoxosulphate(VI) is a way of testing for the presence of water. This colour change is a simple and effective way to detect the presence of water in a substance or environment.