I'm thinking that you won't be able to water cool the ROG Matrix HD 7970. The ROG cards that ASUS puts out (with the exception of the new ARES II) are all fine tuned for being air cooled. That being said, it may be possible to attach a water block to one if you were to disassemble its stock heat sink and fan setup but I do not recommend it unless you're very experienced and are willing to risk damaging the card. If you want to find a card that you can water cool you may want to buy one that is already setup with a water cooling system, or simply by the stock card and find a block that will fit whatever card you choose.