The formula of blue copper (II) sulfate is CuSO4.5H2O
The .5H2O is the water of crystallisation of this familiar hydrated salt.
You can drive off the water by heating hydrated copper (II) sulfate with a Bunsen burner.
‘White’ anhydrous CuSO4 is used as a chemical test for water.
It turns blue when you add water to it.
What other transition metal salt is used as a chemical test for water?
And what colours does its hydrated and anhydrous forms show?