In the conventional water treatment process, filtration usually follows coagulation, flocculation and sedimentation. ... Backwash water volume, gal = 850 gpm x 8 min. Backwash water volume, gal = 6800 gal . Backwash Pumping Rate, gpm. The desired backwash pumping rate (gpm) for a filter depends on the desired backwash rate (gpm/ft …Web