Charge transfer to solvent (CTTS) energies of small halide-water clusters, X-(H2O)(n=1-4) (X=F, Cl, Br, I) have been studied using first-order configuration interaction as well as time dependent discrete Fourier transform density functional methods. The only available experimental data are the recently reported CTTS energies for I-(H2O)(n=1-4) clusters by Johnson and co-workers [D. Serxner, C. E. H. Dessent, and M. A. Johnson, J. Chem. Phys. 105, 7231 (1996)]. These results are in good agreement with our predicted values. The calculated CTTS energies indicate that there is regularity in the change of CTTS energies with respect to the change of halide anion as well as the cluster size. Our investigations have shown that this observed trend of CTTS energies of X-(H2O)(n) clusters could be quantitatively explained by the ionization potential of the halide anions and the binding energies of the respective clusters.