Our food substances, like other matter, are made up of certain definite chemical elements. The simplest food substance is water, in which we have a combination of only two elements, hydrogen and oxygen, twice as much hydrogen as oxygen.

Water plays a large and important part in our life, entering into the structure of all matter, even into what appears to the eye to be dry. Since water makes up two thirds of the weight of the entire body, great care should be exercised to see that plenty is provided with the diet. There should be at least six glasses a day for children and eight glasses a day for adults.

It is also important that the water should be pure, for serious diseases may be introduced into the body through a contaminated water supply. Some of these are typhoid fever, diphtheria, and dysentery. It is never safe to drink from streams and brooks receiving the drainage of a valley; and wells should be placed with great care so as not to get either the surface or the sub-strata drainage from cesspools and barnyards.