Why would you want to water-cool your hard drives? Any larger fan running at 5V will be more than enough and will benefit not only your drives, but all sorts of stuff in your case...
I want a silent enclosure to quite the drive, which will heat the drive up. Since I have a water kit already would be nice to not add fans and use the water to cool. Bare in mind this computer has silent watercooling, fanless PS, water heatsink on the videocard, mobo chipset, and cpu, with 2 120mm fans @ 700rpm.
i dont know of any actutal enclosures combined with water-cooling for your hard drive, however, i think Koolance is one of the only ones to carry hard drive water-cooling devices. maybe you can buy some enclosure and mod it with the Koolance products. But i doo agree with the rest of the guys and say you dont need to cool your hard drive.