The amount of water drunk per diem is usually less than should be taken. Many persons believe that it is injurious to drink much fluid with their meals and forget to take any between, and as a result not enough water is consumed to thoroughly dissolve and eliminate the waste matter of the system. The average quantity of urine voided is 52 ounces, 10 ounces more are lost from the surface of the lungs, and 18 ounces from the skin. This total of 80 ounces must be daily replaced to maintain the equilibrium of the body. The solid food of a mixed diet has been shown above to contain on the average 50 or 60 per cent of water, so that about 25 ounces of water are taken into the system daily as an integral part of the food. In addition, at least 55 ounces or more should be drunk either as plain water or in various beverages.

Another way of stating the above facts is that the average quantity of solid food (not water-free) which is required by adults is between 40 and 45 ounces per diem, and the total amount of food, including all fluids, should be from 95 to 120 ounces, of which three fifths or four fifths is composed of water, and the remaining one or two fifths of water-free substance. These estimates are only intended for general application, and there are necessarily many exceptions.

The ratio of solid to liquid food varies in health with the greater or less preponderance of fluids, the solid being more constant. It is commonly nearly 1 to 2, but many persons reduce it to 1 to 1.5, or even 1 to 1.

Muscular exertion demands an increase in both solid and fluid food, but the former is more essential than the latter, if the exertion be prolonged.

When a man does increasing work, unless his food be proportionately increased, he begins to consume his own tissues until their loss so weakens him that he is obliged to desist from a part, at least, of his labour. Should the disproportion between output and income continue, he becomes so enfeebled as to be liable to the inroads of hardship in various forms - especially those of cold and zymotic diseases.

It is estimated that in each twenty-four hours a man of normal health and physique absorbs, including the respiratory oxygen and water, about 7.25 pounds of material, which he eliminates in a corresponding quantity of waste, about three fifths of which is water.