Our team investigated increasing the water recovery of a membrane desalinating unit by combining the high salt rejection properties of reverse osmosis (RO) membranes with the high flux (production) properties of nanofiltration (NF) membranes. Using both membranes, the overall water recovery can go above 90% by tailoring the salt passage within the system. We developed models simulating hydraulic and physicochemical conditions within the RO/NF system, which are currently not available in commercial modeling software.