Though micro- and ultrafiltration (MF and UF) membranes have recently proven to be very promising technologies for the physical removal of pathogens, they may not meet the standards required by the Enhanced Surface Water Treatment Rule. Reverse osmosis (RO) and nanofiltration (NF) membranes could provide even greater removal efficiencies for pathogens than MF and UF while removing many other components (e.g., disinfection byproducts). One study tested three separate RO membranes and found that the mean removal for MS2 phage virus was between 3.2 and 5.5 logs. They found that an RO membrane could achieve