Yep, you read that right. One of my Supercomputers at MSU is water-cooled. Warm water cooled to be exact. It’s Serial #1 of Cray’s LC-300. She’s about 5 years old now, but still kicking. The cooling fluid inside the racks is actually a Glycol.
There is a CDU in each rack (Coolant Distribution Unit) that circulates the Glycol through the nodes. The Glycol is cooled with the warm-water that itself is cooled from a dry-cooler outside in our equipment yard.