It’s extremely ironic that even though a diver may be surrounded by millions of gallons of water, dehydration can be a serious problem. Dehydration occurs when a diver has inadequate water throughout the body. But why is this a problem? Because, as every Freshman biology major learns, water is essential to a dozen critical biochemical processes and biophysical systems. At the most basic level, water is needed in order for cells to carry out chemical reactions. Tissues require fluid in order to stay plumped and flexible. And water is required in order to produce blood and keep it moving properly throughout the cardiovascular system.
Fluid can be lost through sweat (yes, even underwater) or urination. But the most common and extensive source of water reduction is simply through breathing. Normal breathing expels considerable moisture into the air. That’s obvious when you breath close to a piece of glass. Underwater breathing actually accelerates that effect because the air in scuba tanks is significantly drier than ordinary surface air. Just as heat flows from a warm body to a cooler one, moisture flows from wetter areas to dryer.
One potentially serious result of lowered body fluid concentration is the effect on the blood and muscle tissues. When the body is dehydrated, blood flow is reduced in the tissues. That has a direct effect on the body’s ability to absorb and release nitrogen. That can radically alter the time needed to perform a safe ascent.
In order to avoid decompression sickness a diver has to ascend in a controlled way at no higher rate than 30 feet per minute. Even at that, several stops at various depths on the way up are commonly recommended. The alternative is ‘the bends’ – joint pain, cramps (legs, arms, abdominal, etc) and a number of other nasty consequences. If nitrogen can’t be released at the proper rate, ascents can take longer – and your oxygen may run out. That can leave you with a very unpleasant dilemma.
Less drastic harm can occur from dehydration, which is still unpleasant enough to warrant efforts to avoid. Dehydration produces more rapid fatigue, spoiling your enjoyment and shortening your dive. This happens in part as a result of lowered blood flow, making the heart pump faster.
Fortunately, it’s easy to achieve the proper level of hydration before and after a dive. Depending on your general physical condition and level of activity simply drink plenty of water or a sports drink. But one without tons of sugar. If the weather is warmer, drink more. If you plan to dive longer, drink more. And drink over a longer period of time, giving the body plenty of time to absorb the fluid without overwhelming the kidneys.
Just as important is what to avoid. Don’t drink coffee or other caffeinated drinks like colas for several hours before or after a dive. Never consume alcoholic beverages for several hours before or after a dive. Yes, that sounds like a real party dampener. But being dead is much less fun than being drunk.
Headaches are sometimes caused by inadequate fluid in the blood vessels in the head and neck. Look for that. Test your fluid level by, among other things, examining your urine. It should be light colored to clear before a dive. After the dive, rehydrate slowly.
Dive safely and always use common sense.