Ultrafiltration (UF) of reservoir water for drinking proposes was performed in a crossflow filtration with frequent membrane backwash. The effects of operating condition and raw water quality on UF behavior were investigated. The membrane flux decreases with increasing turbidity and there is a somehow linear relationship between membrane flux and the log of turbidity. Permeate flux increase with increasing the transmembrane pressure (TMP) and the permeate flux increase slightly when the TMP is added to a certain level. Chemical analyses of the permeate water showed that drinking water regulations were fulfilled. UF treatment provided effective turbidity removal. UF membrane also perfectly removes all coliform bacteria. With the exception of one weak positive effect in raw water, the genetoxic activities of raw water and ultrafiltrated water samples are negative.