We do the generic Camco filter, if that's insufficient then we carry a Britta pitcher, if that's not enough we carry 5 gallons of emergency water in a container and can use that until we can get to better water, bottled water, or a better filter system (most likely we'd grab a backpacking filter and fill the Nalgene bottles we always have with us). If it was for 4 months I'd invest in a 3 stage filtering system and put it before the intake.