When blue vitriol is dissolved in water
When a sample of $\ce{CuSO4⋅5H2O}$ is dissolved in water, the $5$ molecules water are mixed with the water used as solvant, and cannot be distinguished any more from the other molecules of water. It does not really matter, as if you want to calculate the molarity, you never dissolve your sample of $\ce{CuSO4·5H2O}$ in exactly $1$ litre water. No ! You dissolve it in a volume of water big enough to get one liter solution, whatever the exact amount of water used for this dissolution. It should be a little less than one liter water. The only important parameter is the final volume of the solution, namely one liter.