Are you familiar with flotation tanks? They're pretty small and only hold a few feet of water, just enough so you can float without touching the bottom of the tank. The water is also incredibly salty, hence the "floatation" part of a flotation tank.

Point being, it would be pretty hard to drown on your own accord in a flotation tank. Perhaps he lost consciousness and drowned, but this would indicate more about Traywick's current state of health than anything else.