Not sure any of these high end servers use water cooling. As an IT pro (for quite a long time now) I've yet to see it used on any professional server, probably because risks are way too big for any data center to allow some kind of water running inside it, any leak and the whole place is at risk. What you gain from it is not worth the risk, simply buying x new servers for the same price is a much better option. Think HP did this long time ago, not sure they still do it now.
From a personal use point of view, water cooling might make sense, when talking about servers, that's usually pointless, modern server rack bays (and rooms) use really efficient and less risky cooling systems. Cooling everything at once through efficient air management system > water cooling... and anyone buying this kind of very high end servers buy a few of them, if you an afford these, you can't afford any down time, so you need back up in case a server fails (where I work right now we have about 10 servers with 1Tb each for the main website + backup + test... and I want to take one back home ;_; ).