Hollow fiber ultrafiltration is used to remove virus, Giardia, Cryptosporidium, and coliform and to reduce turbidity and TOC from surface waters to produce potable water. The application of ultrafiltration technology to the municipal water market is an extension of its success in a myriad of applications. Hollow fiber ultrafiltration membranes can produce consistent filtered water from inconsistent feed water sources without the use of pretreatment. Data will be discussed from four PTS river water sources having various feed water qualities: Boise River (Idaho), Medina River (Texas), Cumberland River (Tennessee), and Wishkah River (State of Washington). Polysulfone membranes are highly chemically resistant and provide a positive barrier, preventing passage of microorganisms from the feed to the filtered water. The skinned construction of the hollow fiber ultrafiltration membrane provides a physical barrier which removes contaminants and separates them from the treated water stream. Long membrane life is ensured by the use of mechanical cleaning techniques, low pressure water backflush, and flow reversal.