In 2011, IBM announced the Power 775 supercomputing node/system which, for the time, was a significant increase in computing performance and energy efficiency. The system was designed from the start with water cooling in mind. The result: a system with greater than 95% of its heat load conducted directly to water and a system that, together with a rear door heat exchanger (HX), removes 100% of its heat load to water with no requirement for room air conditioning. In addition to direct water cooling the processor, the memory, power conversion, and input–output electronics also conduct their heat directly to water. Also included within the framework of the system is a disk storage unit (i.e., disk enclosure) containing an interboard air-to-water HX. The heart of the water cooling system is the water conditioning unit (WCU). The WCU circulates system water at a controlled temperature and flow rate while also transferring the electronics heat load to the data center facility building chilled water (BCW) system. The brain for this system is the motor drive and control assembly (MDA-WCU). In addition to the pump motor drive function, the MDA-WCU contains the control circuitry and associated firmware that maintains system water at a prescribed temperature above the room dew point irrespective of system and or facilities thermal/flow transients. It is also capable of error detection and fault isolation that, together with higher level system firmware, facilitates serviceability, and availability. The paper will present the WCU and MDA-WCU design with an emphasis on the control methodologies and algorithms.