Sorry about you losing your drone. WE all make mistakes, when learning.
Just curious as to what happened, could help sone body else avoid doing the same thing. I have pontoons on my MP's as well, but I don't mess around with water landings. Only for veteran pilots, you never want to get a drop of water inside the battery compartment. Have never heard of a EMERGENCY landing on water going well. Usually, only thing worth saving is the body, and especially if salt water gets inside with the electronics.
I was practicing, with water puddles after a rain, and that made me nervous. I just have them for back up, so it floats, and send the other one to retrieve out of the water.