When something goes wrong with watercooling , it really goes wrong, woke up today and found a green puddle on my table , had to strip down my whole pc and put it back together because of a loose hose clamp from the radiator. Lucky it was the bottom hose.
For graphics cards I'm too scared to water cool them now, I would have done major damage if it leaked from the CPU or GPU.
Not all cooling systems are perfect either , pumps make a humming sound, maintaining the hoses and checking the clamps and topping up the coolant can be fiddly. Most non reference graphics cards come with excellent cooling systems , liquid cooling your GPU's is more of a personal choice these days.