Why you should wet your whistle before and after you dive. Unfortunately, this predicament can have serious consequences for divers. There are several ways in which diving and the underwater environment contribute to dehydration. When a person is dehydrated, there is a reduced volume of blood in the body.
Less volume means less blood flow to the tissues.
This in turn affects the body's ability to wash out waste, such as nitrogen. The result is that a diver surfaces without having off-gassed as efficiently as he would have if he had been well hydrated. Blood flow to certain tissues is further compromised during dehydration by the body's own means of compensating for a low blood volume. To guarantee an adequate supply of blood to vital organs like the brain and kidneys, the body signals blood vessels supplying other parts, like skin and muscles, to clamp down, restricting flow even more. In addition to the increased risk of DCS, dehydration can adversely affect divers in other ways.