348 SCIENCE OF HOME AND COMMUNITY 



wells, and surface water from lakes and rivers. The chief 

 kind of impurity against which the water must be protected 

 is the disease germ. One of the commonest of these germs 

 found in water is the one that causes typhoid fever. Many 

 cases of typhoid are due to impure water. 



How it is made impure. Drinking water may be con- 

 taminated by typhoid germs in a number of ways. In 

 every case some one with typhoid fever is the source of the 

 germs, which are given off in the wastes of the body. Some- 

 times the sewage containing these germs may empty into a 

 river, and then the water from this river may be used as 

 drinking water by a city situated further down the river, as 

 on the Merrimac River in New England. A city may 

 discharge its sewage into a lake and take drinking water from 

 the same lake near the sewer outlet, as was formerly done in 

 Cleveland, Ohio. Even the water of an artesian well has 

 been known to be contaminated through a leak in the water 

 pipes, through which sewage entered when a flooded con- 

 dition of the river brought the river water in contact with 

 these pipes, as happened some years ago in Mankato, Minn. 

 In Plymouth, Pa., an epidemic occurred because a family 

 living on the banks of the stream from which the town took 

 its water had thrown the wastes from a typhoid patient on 

 the snow near the stream. When this melted, the germs 

 were carried into the stream. 



All these cases go to show how important it is to prevent 

 contamination of the water supply, because typhoid is a 

 preventable disease, due to carelessness, and many cases 

 may be avoided by keeping the water supply pure. 



Purification by filter beds. When there is a possibility 

 that water may be polluted, it can be made clean by filter- 

 ing, and this is being done by many cities. Sand filters are 

 the means which modern science has found for purifying 

 water. These filters are four or five feet thick and are 

 spread out over several acres. On top is a layer of fine sand, 



