We're going to dissociate NaCl, and see how many water molecules we need to generate Na+ and Cl-.
Make a Na···Cl system and separate the two atoms
Choose the following setup:
Unrestricted: [Yes]
Spin polarization: 0.0
XC functional: PBE (GGA)
Relativity: Scalar
Basis set: TZP
Frozen core: Small
Numerical quality: Good
Save
Run
Analysis
Go to [SCM]:[Output] to see the output, and then go to [Properties]:[Multipole Derived Charges] to inspect the charges on the atoms
Add explicit water molecules until the separation leads to a cation and an anion.
Further reading
S. Osuna, M. Swart, E.J. Baerends, F.M. Bickelhaupt and M. Solà
"Homolytic versus Heterolytic Dissociation of Alkalimetal Halides. The Effect of Microsolvation" ChemPhysChem2009, 10, 2955-2965
10.1002/cphc.200900480