The water plant for a high temperature reactor must be capable of providing several purities of water to the various components of the installation. The actual treatment methods will depend on the location and size of the reactor, the size and sources of the water and the ease of disposal of radioactive wastes. This document examines the needs for the various water purities. It also defines the area of future work to provide the information necessary for the design of water plants for high temperature reactors or for the conversion of existing reactors to recirculation cooling.