The first thing to ask yourself is: Do you NEED water cooling? Does your computer get so hot that only a dowse down with a (theoretical) hosepipe will keep it cool. Even if it does, have you thought as to why that may be? Is the current cooling system not working properly? If it isn't, get it fixed.
Or is it just that you want to be able to say that your computer is so powerful that you have to have water cooling as a friend of mine does? There are all sorts of heat pipes and fins in bright anodised colours and occasional gurgling noises that seem to generate much excitement when all the machine is doing is some simple video rendering.