Don't wanna be a pain or ruin your plans. But I would recommend you to Get a TITAN X PASCAL and then think of water-cooling it.
Going for custom loop on lower end GPUs is not satisfactory and a waste of money in my opinion.
Assuming that you have good budget try replacing GTX1070 with a GTX1080 or TITAN X PASCAL(TITAN X PASCAL becomes beast when water-cooled).
The gain in performance by doing so will be lot greater than what you get by water-cooling GTX1070.