As said before, use air. HDD don't put out enough heat for it to pose a serious risk due to lack of cooling. Even the high-end 15,000 rpm drives might need a fan. Another waterblock (or in your case, 2 more blocks) would take away from your system (i.e. cpu, gpu, w/e). Sure, it would look badass, but it would probably hurt your system more than it would help it. Until rpms on hdd's are under ~15k, then air cooling will be sufficient. When hdd become more advanced, they will be ready to adapt to water cooling and then it would be useful. Your trying to use technology before it's fully developed. I'm not trying to flame or anything, I just think it's not necessary.