If you were to make a human from scratch you would find that the primary ingredient required would be water. We are approximately 70% water by weight. Water is vastly important to our health and well-being. We can go without food for a month and possibly not die, although the intense suffering starts right after the first missed lunch. However, if you deprive a human of water, the suffering starts at about the same time, but it is much briefer, because death follows in just a few days.
Water deprivation, or dehydration, manifests itself in the species with increased thirst to start, moving on to swollen tongue, weakness, dizziness, heart palpitations, dis-orientation, confusion, and fainting. An overall loss of 5 to 8% of the body's water is enough to bring on mental and physical deterioration.
Where does the water go?
The problem is that we are not water-tight containers. We leak everywhere! Our skin is incredibly porous, and as a temperature regulating design our body squeezes water through it constantly to cool itself by evaporation. This being the well documented and deodorized manifestation called perspiration. This is a variable rate of water loss which is aggravated by increased temperatures, and activity.
Another form of water loss to the body happens through respiration. As the surrounding air is breathed in to supply the body's oxygen needs, the lungs exchange the oxygen for waste gasses and water vapor which are exhaled. This is a continuous and insidious loss of water that is rarely considered.
Add urination to these constant losses along with water evaporating from your eyes, and the saliva left behind on eating utensils, sexual partners, or objects of disgust, you would think that we would dry up and blow away! This is where the desire 'thirst' comes into play, gently reminding us to have a sip of something to replenish our water reserves. With a total lack of scientific evidence we are recommended to consume a couple of quarts of water a day for optimal health.
The sub-species known as Scuba Divers have a unique relationship with water. As a form of recreation they submerge themselves in it for prolonged periods, and at variable depths. Although submerged and surrounded by water, scuba divers have their own specific issues when it comes to dehydration.
Scuba divers subject their bodies to pressure at depth, and with the breathing of compressed air they can subject themselves to a malady called decompression illness. Although correct, safe diving practices and training should keep you from this affliction, one of the best and easiest preventive measures is to keep yourself well-hydrated by drinking plenty of water prior to diving.
As mentioned the mere act of breathing is a point of water loss. Dry air breathed in takes on water in the lungs. It makes sense that if the air is dryer than normal more water is absorbed and carried away as exhalation. The compressed air used by divers is rated at about 24 ppm (parts per million), which is very dry and actually only .094% humidity! Here on Roatan the average humidity hovers around 75% and it's no wonder that switching to breathing from a tank will give you a dry mouth over the course of an hour dive. It is estimated that at 25% humidity, the body loses up to an ounce of water an hour just in respiration at rest on the surface.
Divers are also subjected to Immersion Diuresis.
In this case the body temperature is lowered by the surrounding water and causes constriction of the blood vessels to conserve heat (even here in the tropics), increasing the blood pressure and the conversion of water to urine. Hydrostatic pressure (underwater pressure) also increases blood pressure, causing more water conversion to urine, and lengthening lines at the post-dive restroom.
Water is the recommended beverage for hydration and re-hydration. It has been pointed out that after we are weaned, water is the only liquid our bodies are designed to consume. However the variety of liquids available for consumption blows the mind. Liquids of every color, flavor, level of sweetness, and viscosity exist for our drinking pleasure. Some even have Electrolytes!
Our recommendation is to hydrate well before diving, and over the course of the day to replace all the lost liquids which can help to, avoid decompression illness, and is good for general well-being.
Post-dive rehydration involving beverages supplying calmness, stimulation, and intoxication are some of the local methods, and open for more research at this date.