WATER 



139 



cities require the manufacturers of artificial ice to distill 

 the water before freezing it, in order that it may be free 

 from germs and other impurities. For city use, distilla- 

 tion of water is impracticable because the large quantities 

 of water used would make it too expensive. There is 

 another method which is almost as effective. 



Filtration is a process of purifying water by causing it 

 to flow through sand and gravel. A great number of 

 American cities are using the 

 filtration process of purification. 

 It prevents a great number of 

 diseases, and especially typhoid 

 fever. It also removes some of 

 the harmful chemicals which are 

 in river water. There are small 

 charcoal and stone filters which 



I 



SECTION OF A SAND FILTER 

 Showing impure water (top), 

 sand, gravel, and filtered water. 



can be attached to the water pipes in the private home 

 and the water thus purified by filtration. These filters 



must be cleaned often 

 or they will become a 

 source of disease in- 

 stead of preventing it. 



93. Use of Water 

 While Camping. Since 

 so many of the Ameri- 

 can people are beginning 

 to spend part of their 

 vacation in the open air, 

 along some lake or 

 stream, it is very im- 

 portant that they should 

 be acquainted with some 

 encounter when they use 



A DRIVEN WELL FOR CAMPERS 



of the dangers which they 



