The PCS-Preussag Conversion System(R) is a mobile floating seawater desalination plant supplying potable water to arid coastal regions. In the present design example, a standardized Preussag seawater desalination plant using reverse osmosis technology is preferably installed on a converted single shell oil tanker because this outdated tanker design concept will eventually be outlawed due to its potential ecological hazard in case of emergency. The PCS-Preussag Conversion System((R)) can offer a useful and economic alternative to conventional land-based desalination plants for a number of applications.