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#21
they are self contained units. they come pre filled with water. all you do is attach the radiator to the case and place the block on the cpu. plug in the fan and pump into the mobo and its all fitted!
most companies dont use water, they use an non conductive coolant, so even if it did leak your components wouldn't be in danger.
you dont worry about a cpu fan failing and cooking your cpu, so why worry about a water leak