Exactly what lozz08 said.
Unless you plan on going 2xGTX590's, I wouldn't bother. Even then, if your case is spacey enough for a 240mm, it probably has good enough air circulation to accommodate the 2xGTX590's w/o water cooling.
I water cooled a system out of necessity. It was a huge hassle. Today, you have the luxury of enjoying performance without excessive cooling needs. Enjoy it!
Only exception: you are a hobbist and really want to make something special. Otherwise, don't bother and enjoy your AWESOME gpu