A method is provided for the 
continuous production of treated waters using a staged, tapered array membrane 
plant by a process of process-logic-controlled (PLC) stage or stage increment isolation and removal from service, washing and return-to-service concurrent with the continued operation of all other stages and / or stage increments of the 
plant. Specifically, there are 
plant mounted input / output sensors that supply the PLC with the data required to identify the location and degree of “
fouling” of the individual stages or stage increments of a tapered array membrane 
water treatment plant, where 
fouling is defined as a loss of 
water flow through a 
membrane surface at a given pressure when compared to a 
water flow standard for the surface. When a stage or stage increment of a plant is defined by this process to be “fouled,” the PLC commands the 
initiation of a sequence of automated valve openings and closings to a) remove the fouled stage or stage increment from feed 
water treatment service, b) to flush and wash the stage or stage increment, and c) to return the stage or stage increment to feed 
water treatment service. Optionally the PLC function can be extended to include the 
monitoring and control of ancillary valves and a variable-frequency-drive feed water pump to command the parts of a plant that remain on-line during the process of a stage or stage increment wash to continue to produce more, or less, or volumetrically identical amounts of membrane water treatment process permeate by combinations of valve re-settings, pump speed adjustments, and stage-to-stage intermediate 
water diversion.