This paper presents three studies of post treatment of membrane treatment, with a focus on more than a dozen lessons learned from the following three desalination and groundwater recharge facilities: Clearwater, FL Groundwater Replenishment (GWR) Project, San Antonio Water System (SAWS) Brackish Groundwater Desalination (BGD) Program , Tarpon Springs, FL variable salinity brackish groundwater RO WTP .Post-treatment of membrane processes is an essential step for ensuring compatibility of reverse osmosis permeate with the intended use of the water.