This section is from the book "Practical Dietetics With Special Reference To Diet In Disease", by William Gilman Thompson. Also available from Amazon: Practical Dietetics with Special Reference to Diet in Disease.
It is estimated that water composes about 70 per cent of the entire body weight, and it is an almost universal solvent. Its importance to the system, therefore, cannot be overrated. The elasticity or pliability of muscles, cartilages, and tendons, and even of bones, is in great part due to the water which these tissues contain. As Solis-Cohen says, "the cells of the body are aquatic in their habits." The amount of water required by a healthy man in twenty-four hours is, on the average, between 65 and 70 ounces, besides about 20 ounces taken in as an ingredient of solid food, thus making a total of 85 to 90 ounces. The elimination of this water is divided as follows: 28 per cent through the skin, 20 per cent through the lungs, 50 per cent through the urine, 2 per cent through other secretions and the feces. This is, of course, a very general computation, for there is constant variation in the activity of different organs.
A large proportion of the water is taken in the form of beverages composed chiefly of it, and by many persons they are substituted for plain water altogether. In some countries light wines, beer, and other fermented drinks wholly replace drinking water. This may be due to habit and custom, or to necessity from lack of pure natural water, but in all cases the quantity of water required to maintain the functions of the body in healthful activity remains the same, whether it be drunk pure or in beverages, or taken with succulent fruits and vegetables, or in milk, koumiss, etc.
One of the most universal dietetic failings is neglect to take enough water into the system.
The uses of water in the body may be summarised as follows:
1. It enters into the chemical composition of the tissues.
2. It forms the chief ingredient of all the fluids of the body and maintains their proper degree of dilution.
3. By moistening various surfaces of the body, such as the mucous and serous membranes, it prevents friction and the uncomfortable symptoms which might result from their drying.
4. It furnishes in the blood and lymph a fluid medium by which food may be taken to remote parts of the body and the waste matter removed, thus promoting rapid tissue changes.
5. It serves as a distributer of body heat.
6. It regulates the body temperature by the physical processes of absorption and evaporation.
All protoplasmic activity in cells ceases at once if they become dry. Elementary cells, such as the amoeba, cease to move, to digest, or to show any form of irritability or functional activity when dry, but if water be added to them their functions will be resumed, showing that they have been suspended and not necessarily destroyed.
The taking of much water into the stomach by its mechanical pressure excites peristalsis. One or two tumblerfuls of cold water taken into an empty stomach in the morning on rising favour evacuation of the bowels in this way. The water, moreover, is quickly absorbed and temporarily increases the fulness of the blood vessels. This promotes intestinal secretion and peristalsis. The increased activity of the lower bowel is explained in this way rather than by the idea that the water itself reaches the colon and washes out its contents.
Lukewarm water acts as an emetic if drunk in large quantity. This action fails above 95o F. and below 6o° F., and is most efficient at about 900 F.