Now that we have water (WATER!!!!!!!!!!!! :D), what would be REALLY epic, is diving equipment :D.
Possibly, one of those ancient diving helmets for 200g in the shop, say, doubling or tripling the time you can spend underwater.
Then a proper diving suit, letting you stay underwater for even longer, for say 500g.
Finally, some sort of mystical device letting you stay underwater indefinitely, for 1 plat, or 2000g, or something like that :D
Possibly a set of flippers as well, stopping you sinking more than half a block into water, but still letting you drown :D
Just an idea, I'll probably comment more ideas onto this :P
staying underwater indefinitely does seem like a plat item. otherwise, it would eliminate one of the purposes of water.
As expected, just got a new idea: diving masks, making the water slightly less... blue :P
At the moment, it's a nightmare to try and see ANYTHING through water. Just an idea.