A water cooling system can be installed in the 500D RGB - a little tight depending on the configuration, but it works. I'm writing these lines on a system in this case with a 360 wheel in the front, 240 wheel in the top and a 120 wheel in the back. Corsair offers a configurator where you can find out the components and compatible cooling configuration:
https://www.corsair.com/de...
Have fun assembling :-)