Page:Food and cookery for the sick and convalescent.djvu/79

Rh beverage it should be aërated. Boiled water is freed from all organic impurities and salts of lime are precipitated.

Water for household consumption is derived from five sources:—
 * 1. Rains.
 * 2. Rivers.
 * 3. Surface water and shallow wells.
 * 4. Deep Artesian wells.
 * 5. Springs.

In many large towns and cities a system of reservoirs has been built, fed by springs and streams which have greatly improved water supplies.

Where well water is used, especial attention should be given to the location of the well. It must be of sufficient distance from drains, cesspools, and barnyards to prevent contamination.

Water drawn from large ponds, lakes, or rivers having a bottom of rock, clay, or gravel, usually furnishes a safe supply. The law, nevertheless, requires frequent analyses—thus helping, as far as possible, to make healthful conditions prevail.

Water is frequently spoken of as hard or soft. Hard water contains mineral matter to a greater extent than soft water, the amount varying from eight to seventy grains to the gallon.

The hardness is due principally to salts of lime and magnesia. Soft water is free from an excess of these salts, containing but three to four grains to the gallon. Water is the greatest known solvent, and the softer the water the greater its solvent power.

32° F Freezing point.

32 to 65° F Cold.

65 to 92° F Tepid.

92 to 100° F Warm.

100° F. and over Hot.

185° F Simmering point.

212° F Boiling point (sea level).