JimmySmoke,
There are many different types of water cooling.
Custom: A DIY loop, connecting anything that you can buy a water block for e.g (RAM,CPU,GPU,Northbridge)
Custom are really expensive, and rarely done for their cooling efforts. Although they are very good at cooling hardware, the purchasing of radiators,water blocks,tubing, and fittings can make a VERY inefficient Cooling to Cost ratio.
Example:http://www.newegg.com/Product/Product.aspx?Item=9SIA6ZP...
AIO's: Standing for "All In One's" are prebuilt, water-cooling loops, that can be expanded on traditional only include a CPU water block with a pump, and a radiator. These offer a BETTER Cooling to Cost ratio, but can get quite expensive.
Example: Your h100i GTX
Expandable AIO: Are just like AIO coolers, and usually come prebuilt with a pump/reservoir,CPU block and radiator. They are quite expensive but can be worth it as they allow for expandability.
These can be a cheaper way of making a custom loop.
Example: http://www.ekwb.com/predator/
Since you already have an AIO (not expandable loop) for your CPU theres not much you can do.
You can set up a full custom loop for your GPUs only, although I doubt there will be enough radiator space to water-cool them efficantaly.
You can remove the AIO on your CPU, and create a full water cooled loop (CPU,GPU, radiator) but thats basically wasting your AIO.
Its kinda tough, Id suggest keeping them Air-cooled, unless your prepared to fork out hundreds on dollars for a full custom loop.