The Mount Pleasant Waterworks (MPW) of Mount Pleasant, South Carolina, operatesthree reverse osmosis (RO) water treatment plants, with a total capacity ofapproximately 5 million gallons per day (mgd), using the Middendorf Aquifer as asource. These three plants were constructed in the early 1990s and the membranesthey use may be reaching the end of their useful lives. In an effort to reducecosts and maximize production capacity, the MPW evaluated new low pressure ROmembranes for use in their existing water treatment plants (WTPs). Recentadvances in the production of composite membranes have led to the development ofnew low pressure RO membranes. These membranes offer similar salt rejection andan increased permeability (i.e., 0.30 gfd/psi compared to 0.19 gfd/psi) comparedto their predecessors. Additionally, new 400 ft2 , 8-inch by 40-inch elements arenow available. Implementing these membranes offers the ability to increaseproduction capacity if hydraulics are not limiting. Increased permeability is acomplicated issue associated with the use of these new low pressure ROmembranes. Increased permeability results in poor flow distributions and requirescareful hydraulic consideration. Excess product flow from first stage membraneelements (i.e., in a multi-stage array) results in lower flows to subsequentstages. Element recoveries and concentration polarization factors must be lessthan 18% and 1.2, respectively in order to prevent membrane fouling. Hydraulicremedies for distributing flow evenly between stages in a low pressure ROmembrane array include: permeate throttling; interstage boosting; and, hybridmembrane installations. In the case of Mount Pleasant, infrastructure isexisting, pumps are sized for traditional (high pressure) brackish watermembranes, and membrane equipment may be difficult to alter. This study consistedof pilot testing various low pressure RO membranes from multiple suppliers.Modeling and cost analyses were conducted to determine the most economical way toimplement low pressure RO. This approach to low pressure RO implementation andcompetitive procurement is anticipated to save Mount Pleasant approximately $1million over the next ten years in operation and maintenance savings. Includes 11 references, tables, figures.