Water in the Human Body.—Taken as a whole, the human body consists of about seventy-one parts of water in the hundred. When we consider how large a quantity of water is given off daily, not only through the kidneys and intestines, but through perspiration, sensible and insensible, and through the vapor breathed out from the lungs, it becomes clear that the food must contain a large proportion of water to supply the daily loss.

The proportions of water are not always quite the same, nor does the identical water present in any part of the body at any given moment remain there. There is a constant movement, a continual renewal going on in the body, and water helps to accomplish this renewal. By means of the watery substances, the saliva, the bile, and other juices of the stomach and intestines, the solid nutritive parts of the food are dissolved, and pass into the blood to renew the waste, and to keep up that continual current called life. Water is also useful in carrying off the worn out and useless materials which pass out through the fluid excretions and through the vapors from the lungs and skin.

Water in Food.—The amount of water contained in many articles of food that appear quite solid is generally surprising to those unacquainted with the chemistry of foods. In one hundred pounds by weight, fresh oatmeal contains 5 pounds of water. Corn and barley meal, wheat flour, peas, and beans contain 14 pounds; rice 15; bread 40; potatoes 75; grapes 80; parsnips 81; beets 82; apples 83; carrots and cabbages 89; onions 91; lettuce 96.

Of the animal foods, butter contains 10 pounds of water in one hundred; bacon 22; cheese 34; eggs 72; lean meat 73; fish 74; milk 86. By cooking, most foods lose a part of their natural moisture. The eatable part of a mutton chop contains 70 per cent of water before cooking, and 54 per cent after.

Daily Requirement.—Scientific sanitarians have estimated the daily requirement of water for a person at from twelve to sixteen gallons. The British War Department aims to provide each soldier with fifteen gallons daily. In cities the daily allowance per capita is fifty gallons and upwards, which provides for animals, manufacturing purposes, fires, sewerage, etc., as well as for drinking, cooking, bathing, and other wants of man.

Sources of Supply.—The importance of an abundant supply of pure water is becoming more and more apparent each year. The numerous and serious epidemics throughout the country whose sources have been traced to the use of impure water leave no room for question on this point. Most cities draw their supplies from rivers and lakes. If these sources are kept free from sewage and the waste of manufacturing establishments the water is likely to be pure and wholesome. Subsiding reservoirs and filtration beds are needed to take out the mud occasioned by rains, and to catch up whatever floating matter may be carried into the basins. Muddiness is not always an indication of unwholesomeness, nor is clearness a proof of purity. Germs of disease have been found in the clearest water. Whenever there is the least suspicion of unwholesomeness, all water used for cooking and drinking should be boiled. It is not safe to trust to the theory, held by some, that a running stream, even if polluted, will in flowing a distance of twelve or fifteen miles purify itself.

Wells, which are the chief source of supply in the country, should be kept away from barnyards, stables, cesspools, and the waste waters from dairy and kitchen, to preserve them from pollution. Many cases of typhoid fever and other serious diseases have been directly traced to a violation of this rule. The ground surrounding the well should be raised so as to throw all surface water twelve or fifteen feet away from the well. See also what is said on this subject in the chapter on Dwellings.

Springs usually furnish the purest and best water. Coming from a considerable depth, spring-water loses, in its passage through the earth, most if not all its organic matter, and rises to the surface clear, cool, pure, and sparkling. The spring should be walled and covered, and otherwise protected from surface drainage.

Cisterns.—Rain-water collected in the country, and under favorable conditions, is comparatively pure and wholesome. In the cities, it contains such a large amount of organic matter and other impurities, washed out of the air and off the roofs by the rain and snow, that it is generally unfit for drinking without being filtered. On account of its softness, rain-water is very desirable for washing and other domestic purposes, but owing to the absence of mineral constituents it is flat and insipid to the taste. In New Orleans and other southern cities, where cisterns are largely used, the water is rendered cool and palatable by the use of large quantities of artificial ice.

Ice.—It was formerly supposed that in the process of freezing all deleterious matter contained in the water was excluded. Several outbreaks of disease in New England led to an investigation, which showed that the ice used had been taken from ponds whose waters contained large quantities of sewage and other impurities. A change in the source of the ice supply resulted in an immediate check of the disease. Recent research has shown that typhoid bacilli, after being frozen in a block of ice for 103 days, may still be alive when released.

Diseases Caused by Drinking Polluted Water.—A polluted water supply affects not one, but usually many persons, and notable epidemics have resulted. In consequence, more diligent inquiry has been instituted by Municipal, State, and National Boards of Health, and the evidence adduced is of the most positive character. Typhoid fever, cholera, dysentery, and diarrhoea have been clearly traced to the use of impure drinking water, and other related diseases are suspected of having a similar origin, although the evidence is not so conclusive.

Appearance.—A drinking water should be clear and bright. When shaken in a glass or bottle, bubbles should rise quickly and break immediately. If the bubbles move slowly, or seem to hang for some time in the water, they are probably due to the presence of decaying organic matter, and the water is of questionable purity. A slight cloudiness in the appearance of the water, following a rain, may be due to the presence of a small quantity of earthy matter, and not seriously affect its wholesomeness, but if the discoloration looks like that occasioned by a drop of milk the water should be avoided until carefully tested.

Smell.—A good water should have no smell. To this end, the cisterns or other receptacles must be kept perfectly clean. The purest and best waters will soon become foul if stored in unclean vessels.

Taste.—Water having a disagreeable taste is apt to be unwholesome. In order that we may derive from it proper nourishment, water, like other parts of our food, should be pleasant to the taste. And yet, the taste is by no means a satisfactory test of purity. The purest of all water is distilled water, which, by reason of the absence of all mineral matter and air, has a flat and insipid taste. The cleanest rain-water is also insipid. Boiled water is not much better, for while the boiling process may have destroyed all poisonous or noxious germs, and rendered the water absolutely wholesome, it also drove off the natural gases which gave to the water a pleasant taste. Boiled water may be re-aerated by pouring from an ordinary sprinkling can several times.

Hard Water.—Hardness is a serious drawback, whether the water be used for cooking, bathing, or for washing clothes. Food cooked by boiling in hard water is, as a rule, not so well prepared. Greens take on a gray color. Tea is never so good made from hard water. For cleaning the skin, hard water is not nearly so efficient as soft. Linens are never of a good color when washed in hard water.

Boiling hard water before using it improves it. A pinch or two of carbonate of soda, or of borax, is helpful in washing. A little table salt improves it for cooking most vegetables.

Filtration.—The following is a simple home-made filter. Take a large flower-pot, and soak it thoroughly in clean water. Stop up the hole in the bottom with a cork, in which insert a glass tube about three or four inches long. The top of the cork and tube should be nearly flat with the inside bottom of the pot. Put in a layer of sharp, clean sand about two inches deep, then two inches of small gravel, and three inches of well-burnt animal charcoal. On the top of this another layer of sand, and then another layer of gravel. The gravel, sand, and charcoal should be thoroughly washed before using. If the flow of water is too rapid, it may be checked by laying several flat pieces of glass upon the layers of sand. At reasonable intervals, the sand, gravel, and charcoal must be taken out, washed thoroughly, heated in the oven, and replaced in the pot, which must also be soaked in boiling water. This filter will remove nearly or quite all of the inorganic matter held in suspension in the water, but it is not to be depended upon to remove dangerous microbes and other germs of disease. If the water be thoroughly boiled for half an hour and cooled before being filtered, all danger will be removed.

There are many inexpensive filters on the market. They all become clogged, in a little while, and need to be cleaned or renewed. The cleaning of the one described above is so simple that any housekeeper could do it satisfactorily.