How long can a person live if his body (except his head) is placed in water, while he is regularly fed and maintained at a comfortable water temperature?

Natasha Agafonova gave the most accurate answer. More detailed on the same topic:

"The approximate timing of the stages of maceration for the skin of an adult at a water temperature of 20 - 22 degrees:

1. The swelling stage begins after a few hours of contact.

2. The stage of separation of the epidermis occurs on the 4th - 5th day of stay in the water.

Maceration of the skin at the stage of swelling of the epidermis is not a threat. If a person has been in the water for several hours, then the phenomena of maceration will disappear by themselves after a while. After being in water for 24 hours, it may take several days for the skin to regenerate. If, for some reason, maceration has reached the stage of epidermal rejection, the help of a dermatologist, surgeon and infectious disease specialist may be required. It may be necessary to remove the separated layer of the epidermis. The process of restoring the normal appearance of the skin in this case can take several weeks. "

The information is taken from here: Maceration of the skin - causes, symptoms, consequences, treatment, photo

Thus, a person risks dying from infection if left in water long enough.

But after all, the phenomenon of maceration has not been canceled. By 4-5 days, there is a complete rejection of the epidermis, an immunosuppressive state and, accordingly, infection with everything that "comes to hand".

There is such a thing called a "waterproofing bath". It was invented in 1954 by neurophysiologist John Cannigum Lilly, author of The Cyclone Center. The model described in your question is, in fact, such a bath. True, the water tank is placed in a dark soundproof chamber. Water temperature +34 degrees. C is felt as neutral - neither cold nor warm, and the body in it becomes, as it were, weightless. Changes in temperature and humidity disappear, the force of gravity is neutralized. Lilly designed a special soft face mask, the breathing mixture was supplied through a hose.

So, when immersed in this bath, after a while a person begins to plunge into altered states of consciousness, being isolated from external stimuli. Even urination begins to occur with a well-defined frequency (approximately every 15 minutes).

Now the option of such a bath is offered to clients already in psychology and spas: the so-called float cabins (float) - sensory deprivation cabins .

So, from a certain point of view, when entering a certain state of consciousness, a person immersed in such a bath can discover the "true eternity" of his life :).