A single cell electrochemical reactor that utilizes a proton exchange membrane (PEM) as a solid electrolyte is being investigated and developed at Texas A&M University for post-treatment of reclaimed waters with low or negligible electrolyte content. Post-treatment is a final polishing of reclaimed waste waters prior to reuse and constitutes removing organic impurities at levels as high as 100 ppm to <500 ppb total organic carbon (TOC) content and provides disinfection. The system does not utilize or produce either expendable hardware components or chemicals and has no moving parts. This paper discusses a single cell reactor concept; test system design; the role of the proton exchange membrane; and the principle of organic impurity oxidation at PEM interfacial reaction zones. The fabrication performance evaluation; design and sizing of a prototype system are discussed. Test data and kinetic analysis are presented. The feasibility and application for water reclamation processes in controlled ecological environments (e.g., lunar/Mars habitats) are also presented. Test results show that the electrochemical single cell reactor provides effective post- treatment.