HOW COMMUNITIES OBTAIN PURE WATER 



63 



From this table it can be seen that providing the 

 water for a large city is a real problem. 



How do persons who live in the country or in small 

 towns secure an adequate water supply? The most 

 common method of securing water for the country 

 home is from wells and cisterns. This method is used 

 also in many towns and villages and in some large 

 cities. Because water from wells very often becomes 

 impure and harmful it is important that you learn 

 something about the causes and how they may be 

 prevented. 



Wells are of two types, the dug or shallow well and 

 the driven well. The dug well is generally used where 

 the source of water is near the surface and only earth 

 needs to be penetrated to reach it. A driven well may 

 also be used in this way, but it is more frequently 

 used where the source of water is far below the sur- 

 face. Then rock, as well as earth, sand, and gravel, 

 must be penetrated to reach it. Figures 95 and 96 

 show methods of making both types of well. 



The cistern is a tank or reservoir into which rain 

 water from the eaves of the house is run. Water is ob- 

 tained from it by means of pumps. Since cistern 

 water is not hard, it is excellent for cleansing use. 



Water which seeps into the ground penetrates 

 soil, sand, and in some cases layers of porous rock. 

 In this way it is freed of many of its impurities. Such 

 water will pass downward until it strikes solid rock, 

 when it can go no farther. This forms what is com- 

 monly termed the water table. Water that has filtered 

 through to the water table is not always pure because 

 sewage and drainage from barnyards may also drain 

 into it. Figure 97 shows the water table and how it 

 may be contaminated 1 by drainage. Because of such 



1 Contaminated, infected; befouled; polluted. 



FIG. 97. A POORLY SITUATED WELL 



The construction of a shallow well is as important 

 as its location, inasmuch as a poorly constructed well 

 may allow surface drainage to seep into it and make 

 the water unfit for drinking. A properly constructed 

 well of this type should have an uncemented wall ex- 

 tending up several feet from the bottom and cemented 

 brick or stone the remainder of the way to -the top. 

 The curbing should be tight, permitting no surface 

 water to drain into the well. Figure 98 shows a prop- 

 erly constructed shallow well and one of poor con- 

 struction. 



In many places deep driven wells are used for the 

 water supply. These provide a satisfactory source be- 

 cause the water has been well filtered by soil, sand, 



WELL CONSTRUCTED 

 WELL 



POORLY CONSTRUCTED 

 WELL 



FIG. 98 



FIG. 95. MAKING A 

 DUG WELL 



FIG. 96. MAKING A 

 DRILLED WELL 



gravel, and in some cases porous rock. Water will rise 

 to the higher point in the water table when a pipe 

 is driven down to its level. Figure 99 shows clearly 

 how this happens. 



