The spherical solid model and the spin density functional formalism have been applied to calculate the screening of a positive point charge at different lattice sites in Al, Na and Cu. Results are obtained for the Knight shift, the electric field gradient, the heat of solution and the diffusion barrier. It is found essential to use the spin-polarised form to evaluate the Knight shift, especially at low metallic densities and for impurities with a high nuclear charge. Both the Knight shift and the electric field gradient are found to be markedly different for substitutional and interstitial positions. The calculated heat of solution of hydrogen is lowest for the octahedral position in FCC Al and for the tetrahedral position in BCC Na, indicating that no hydrogen trapping at vacancies occurs in these metals.