Abstract: Apparatus for separating an undesired foreign fluid, such as water, from the working fluid, such as ammonia, in a low temperature difference power plant which includes an evaporator and a condensor. A flash separator unit vaporizes the working fluid and separates it from the undesired foreign fluid. The vaporized working fluid is condensed in the condensor. The undesired foreign fluid is accumulated in the evaporator from which it can then be removed. In an alternative embodiment, the separated foreign fluid and liquid ammonia collected in the flash separator unit are not returned to the evaporator, but instead, are coupled back into the flash separator where the separated foreign fluid accumulates so that at the end of the separation process, the undesired foreign fluid can be removed from the flash separator. An alternative embodiment enables the power generating system to continue in operation, although with a decreased capacity during the fluid separation process.