Should you drink water, in wich a dead body was/is in?
Short answer: Nope
Long answer: The human itselfe is not the problem. Because a body that died out of the water is decaying. That means the body becomes carbon dioxide, water and urea. None of those are harmfull to persons in resonable amounts. A water-corpse on the other hand is not decaying, but rotting. The key difference is the oxigen, that a water-corpse doesn’t get. So instead of water, carbon dioxide and urea it becomes a lot of other things, including propionic acid, acetic acid, butyric acid and ethanol, but also substances like cadaverin, which is btw also found in sperm and is kinda toxic, or putrescine which is really toxic. That means, that eating a water-corpse, or drinking the water it has lain in, is definitely worse then eating a normal corpse. You should be aware though, that because humans are relatively big beings, the oxigen doesn’t reach the inside of the body. Meaning that in the middle, there is the same procedure going on as everywere in a water-corpse.
Source: It was basically all from Wikipedia (sorry fifth grade teachers) but since I had to do a lot of clicking around, I thought why not sum it up.