Do water coolers cool CPU and gpu?

Solution
EK make an aio which has quick release connectors to allow you to add other blocks, like gpu blocks to it, it's not cheap though.

It's called EK-XLC predator {with QDC)
By water cooler, do you mean an AIO, or a custom loop? If you're buying a product that has the radiator, tubing all done out of the box, then it's an AIO. As far as I know AIOs are only for CPU, unless you use an NZXT Kraken G10 or G12 to cool the GPU using an AIO as well. So, if you have an AIO, chances are you can't have water cooling for the GPU. However, there are GPUs that come with liquid cooling, but those are very expensive as well. So, the next thing is custom loop. A custom loop does in fact allow you to liquid cool your GPU, so if that's what you meant, then yes you can do it.

It'd be easier for me to help you if you mention a specific product when you say 'water cooler', because there's tons of types of water cooler out there, and all have different specifications. Knowing a specific product, I can tell you whether it'll cool both CPU and GPU, or just one.