The secondary valency and the number of hydrogen bonded water molecule(s) in CuSO 4 · 5 H 2 O ,…

In ${\mathrm{CuSO}}_4.5{\mathrm{H}}_2\mathrm{O}$, $\mathrm{Cu}$ is coordinated with 4 water molecules and two more oxygen atoms from Sulphate ion.

Now fifth water molecule is hydrogen-bonded and is deeply embedded in a crystal. It is not coordinated.

Only 4 water molecules are coordinated and the fifth is the only hydrogen bonded.