Water (H2O) is a transparent, odorless, tasteless liquid. It is derived from five sources,—rains, rivers, surface-water or shallow wells, deep wells, and springs. Water is never found pure in nature; it is nearly pure when gathered in an open field, after a heavy rainfall, or from springs. For town and city supply, surface-water is furnished by some adjacent pond or lake. Samples of such water are carefully and frequently analyzed, to make sure that it is not polluted with disease germs. The hardness of water depends upon the amount of salts of lime and magnesia which it contains. Soft water is free from objectionable salts, and is preferable for household purposes. Hard water may be softened by boiling, or by the addition of a small amount of bicarbonate of soda (NaHCO3). Water freezes at a temperature of 32° F., boils at 212° F.; when bubbles appear on the surface and burst, the boiling-point is reached. In high altitudes water boils at a lower temperature. From 32° to 65° F. water is termed cold; from 65° to 92° F. tepid; 92° to 100° F. warm; over that temperature, hot. Boiled water is freed from all organic impurities, and salts of lime are precipitated; it does not ferment, and is a valuable antiseptic. Hot water is more stimulating than cold, and is of use taken on an empty stomach, while at a temperature of from 60° to 95° F. it is used as an emetic; 90° F. being the most favorable temperature.
Distilled water is chemically pure and is always used for medicinal purposes. It is flat and insipid to the taste, having been deprived of its atmospheric gases. There are many charged, carbonized, and mineral spring waters bottled and put on the market; many of these are used as agreeable table beverages. Examples: Soda water, Apollinaris, Poland, Seltzer, and Vichy. Some contain minerals of medicinal value. Examples: Lithia, saline, and sulphur waters.