The worst thing that can happen to any water-cooled PC is a leak.
This rare emergency can occur and has the potential to cause hundreds of dollars worth of damage, depending on your response. Liquid can escape a closed loop through a loose fitting, cracked tube or block. That is why it's especially important to triple-check a loop once it's finished and perform a test run with distilled water for around 24 hours.
Spotted a leak? Don't freak out! Each and every second is precious, but here's what to do:
Full story from the WindowsCentral blog...