Mobile reverse osmosis water purification units (ROWPU) have been used by the U.S. military with polyamide spiral-wound membrane elements for over a decade to produce potable water for field applications. Although advances have greatly enhanced performance, improvement of the stability of present membranes to oxidizing agents such as chlorine to reduce fouling, increase membrane life and reduce operating costs is required. Recently, a new polyamide membrane, based on the reaction of the cis,trans,cis,trans isomer of 1,2,3,4-cyclopentanetetracarboxylic acid chloride with m-phenylenediamine has demonstrated the ability to withstand high concentrations of chlorine in immersion tests without detrimental effects. The contact time was 30,000 mg/L-hr, (~6.8 years) of exposure at the 0.5 mg/L level. However, in field testing, the polyamide barrier showed a tendency to detach from the support membrane with plant shutdowns. The acid chloride, with its six sterioisomers, was synthesized and the ctct-isomer isolated at >99.5% purity to develop the membrane; the yield was only ~20%. To make the process commercially viable, the purification process will be improved to increase the yield to >90%. Membrane delamination and increased hydrophobicity of the surface of the membrane by a post-treatment step to reduce membrane fouling are also addressed in this proposed program. The total worldwide market for ROWPU-type RO spiral-wound elements, for both military and the private sector, is in excess of $200 million/year. Approximately 75% of this total is produced by U.S. companies. Since most membrane manufacturers are U.S. based companies, any product improvement will further strengthen their position in both domestic and overseas markets. The potential use of the proposed membrane improvements by the Federal Government should provide considerable cost savings in element replacement as well as provide increased efficiency in system operation due to minimized fouling and less frequent need for cleaning. Since ROWPU membrane elements are purchased in large quantities, detrimental effects of long term storage also will be minimized. U.S. membrane companies will benefit in the same manner as the Federal Government, although possibly to a greater extent since the largest part of their market is in the private sector.