Adding to the above, a person will die of hypothermia, even in warm water, because he will give off heat until his body temperature is equal to the temperature of the water.
You can add that if the water is hot, you can boil :)
And if it is warm, then the skin of the hands, for example, begins to swell and look like Shar Pei skin and takes on an unnaturally white matte look, so terrible that the experiment has to be stopped ...
The question is what kind of water. If the water is sea water (hypertonic solution), then after a certain time the person will begin to dehydrate, due to the fact that the water will begin to leave the human body along the concentration gradient, loss of strength, fainting, and even death. If the water is river water (hypotonic solution), then after a long stay, the human tissues will begin to swell, swell, cramps, numbness of the extremities will begin, which is why it is possible to drown. Upon arrival in pure saline, the tissues simply get wet, but they do not change.
It's the same if you drink a lot of water - nothing. Water is the basis of life, a human fetus develops in water for 9 months and nothing bad will become with it.