The removal of hepatitis A virus (HAV) and rotavirus (RV) from source water was studied by means of laboratory and pilot-scale treatment, including coagulation, filtration, and softening. Poliovirus (PV) was included as a frame of reference because considerable data are available on the removal of this virus during treatment. The authors conclude that coagulation and flocculation remove HAV and RV as effectively as PV, with turbidity and alkalinity having no influence on the extent of removal. In addition, all three viruses were found to be efficiently removed during Ca2+ and Mg2+ hardness reduction at pH 11. Coagulation, settling, and filtration in a pilot plant lowered the densities of HAV, RV, and PV by 98.4-99.7 percent. Includes 44 references, tables, figures.