I've replied in the other thread over in Cpu/components but I'd add to Rubix' post,
any company that would do that (not that I know of any who offer such a service)
would have a disclaimer like:
We strive to ensure the highest standards of quality here at XXXPc builders, however watercooling carries an inherent risk to it,
Upon receiving your Watercooled Pc from us please ensure you check all connections for security and signs of leaks,
and do not turn the system on if you suspect any leaks have occurred,
XXXPc builders will not be held responsible for any damage caused to hardware as a result of a leak,
Thankyou for using XXXPc!
Standardised copout paragraph that basically says you wanted water in there, you are responsible for it.
Which is why, as rubix said, you really are better off, both financially and practically, learning to build, install and maintain the loop yourself,
Don't be scared, theres a few of us here to help you along the way
Moto