In order to determine the effects of pH levels, ionic concentrations and polymer dosages on surface chemical properties and the efficiencies of sand filters, a study was conducted using 2 anionic, 2 cationic, and 2 nonionic polymers. Filtration of kaolinite suspensions with sand that had been pretreated with polymers was studied to describe the effects of the presence of Na+, Ca++ and Mg++ ions at different pH levels and at approximately constant ionic strength on particle capture and hence, turbidity removal. Zeta potentials of kaolinite particles and filter sands were determined to help clarify the mechanisms of particle capture in sand filtration. Adsorption of polymers by sand was also measured. The results show that Ca++ and Mg++ ions have a significant effect on removal of kaolinite turbidity by polymer treated filter sand. Calcium and Mg++ ions enhance turbidity removal for all polymer treatments. The enhancement was greatest for anionic polymers and least for cationic ones. There was no significant removal of turbidity in the absence of Ca++ and Mg++ ions when using highly anionic polymer. Zeta potential measurements showed that cationic polymer pretreatment reversed the zeta potential of sand from negative to positive, thus making conditions favorable for the attachment of kaolinite particles (negatively charged) to the surface of the filter sand. The presence of Ca++ and Mg++ ions has no effect on the zeta potential of cationic polymer treated sand and thus not much effect on turbidity removal. The increased effectiveness of turbidity removal obtained with cationic polymer pretreatment indicates that electrostatic forces are dominant.