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.
The object of boiling the water which is to be used for drinking purposes, or in the preparation of food, is to free it from all organic impurities, and in some cases to precipitate salts of lime. There are no forms of germs, and there are no ferments which are not killed by a longer or shorter exposure to the temperature of boiling water. The process consists in the application of heat to water in sufficient degree to expand the air which it naturally absorbs and cause it to rise to the surface in bubbles of various sizes. If the water contains gases of decomposition they are expelled, and the odour is most foul just before the boiling point is reached; later it passes off, showing when the water is fit to drink. When boiled water, cooled, is drunk it tastes "flat" or insipid, but it may be freshened by pouring it through the air from one vessel to another or by shaking it with air in a carafe. Water should always be boiled before being drunk if there is the slightest suspicion as to its purity.
The population of the larger Chinese cities is exceedingly dense, and the water used by the inhabitants is impregnated with all manner of filth, but it is believed that the custom of the natives of drinking tea infused with boiling water, or even drinking hot water, protects them to a great extent from the ravages of certain microbic diseases.
The special dietetic uses of water will receive attention under the appropriate headings of different diseases.
Water may be of service to eliminate waste in various renal diseases, gout, lithiasis, oxaluria, renal inadequacy, fevers, and infectious diseases. If imbibed too freely with meals it lessens the activity of the saliva and gastric juice. Water taken near the end of the gastric digestion of a meal (i. e., two or three hours after taking food) serves to dilute the contents of the stomach and wash it more easily into the intestine. If stomach digestion has been slow and feeble, so that the whole process has been greatly prolonged, the drinking of six or eight ounces of water, either hot or cold, two hours or more after taking food will facilitate its digestion. Water is highly useful in constipation, and it is more quickly absorbed from the stomach when the tension in the gastric vessels is low.
It is to be restricted in dilatation of the stomach, the secretion of weak gastric juice, and sometimes, but not always, in diabetes insipidus, diabetes mellitus, ascites and other dropsies, anasarca, and in some forms of heart disease and obesity.
The daily quantity of water ordinarily drunk varies between two and a half and four pints. About one and a half pint more is taken in the food, and four and a half or five pints are therefore lost through the emunctories.
Foods which contain most water are milk and succulent fruits, such as grapes, oranges, grape fruit, lemons, watermelons, etc., and vegetables like the tomato, squash, and many others of tropical origin. All vegetables contain more water than meats, and many, but not all, ripe fruits contain more than vegetables.