Water cooling uses Distilled Water. If your CPU ever hit 100*C, it would pretty much self destruct, and if it even reached 100*C with water cooling, you have some big issues. Decent water cooling that takes care of the GPUs to costs in the $300-400 range, for a lot less you could get a Thermaltake Big Typhoon cpu heatsing with a silent 120MM fan, a Zalman vf900 for the GPUs and a few silent 120MM case fans. Water cooling still needs fans...and to cool everything, GPUs, CPU, etc.. you will need a big radiator, like a 2 fan or possible 3 fan version... For nearly the same cooling performence just get a good air cooling setup thats silent.
EDIT: If you get annoyed by HDDs or PSUs with nearly silent fans,seak help