MND is still "associated" with the water element, and shows up on water-based items, but there's no added effect to heals by increasing water affinity and no added effect to water damage potency by increasing MND, so that whole argument is pretty pointless. It's just everyone used to seeing the pairings of fire-STR, earth-VIT, water-MND, etc. that makes people think there is something more, but there isn't currently.
Anyhoo, I have faith that SE will bring the beloved water and flood back in whatever form, either post-level 50 or on a new class/job (I always think of Sages and Bishops from FF tactics with the water/aero spells,..... though I will admit BLM only having fire, ice, lightning is pretty old-school FF, haha)