The electronic structure of NaCl–w n (w≡H 2 O and n=1–6, 8) clusters was investigated by ab initio and time dependent density functional theory calculations. Upon photoexcitation, when n<5 the electronic density migrates from one of the Cl valence p orbitals to the Na atom. When n⩾5, the electronic density associated with one of these orbitals delocalizes over the nearby water molecules indicating the formation of CTTS states in the clusters. When n⩾6, contact ion-pair (CIP) and solvent separated ion-pair (SSIP) structures are found. The onset of charge separation in the ground state of small NaCl–water clusters seems to coincide with the formation of CTTS states upon photoexcitation.