A lot of the high-end datacenter racks are getting water cooling now—you have a unit in the base of the rack that distributes water to all the servers above with a couple redundant pumps/PSUs.

Some systems are even water cooling random little components for completely fanless 1U/2U servers... I wonder about the longevity of those systems though!

With the water cooling, you can pipe all that water out to chillers and at a certain heat volume it makes more sense than handling all the heat in air exchangers.