How the power generation industry uses portable exchange DI service to provide demineralized makeup water. Economics are discussed. Regional portable exchange deionization (PEDI) service companies provide external regeneration of exchange tanks or user-owned vessels. This service covers flows to several hundred GPM and effluent quality up to 18 megohm, low TOC polishing mixed beds. Power generation plants are finding advantages utilizing these service companies to regenerate their mixed bed DI polishers off- site, especially when RO units and/or other bulk ion removal systems are involved. Technical, economic and environmental issues will be discussed as well as the structure of a regional PEDI company.