Osmotic backwash may be induced when the feed-side osmotic pressure exceeds the
applied hydraulic pressure across the membrane. It is based on water back flow from the
permeate side to the feed side driven by osmotic forces or salt (mainly NaCl) concentration
differences between both sides of the RO membranes. When water enters the feed channel, it
dilutes the concentration polarization (CP) layer and helps in cleaning the membrane
surface to resume its original flow rate