200 Introduction to the Study of Science 



a location which is altogether satisfactory and with proper care 

 will provide a safe water. 



As the diagrams show, the surface may be taken as indicating 

 the subsoil drainage, but the subsoil slope should be definitely 

 known before locating a shallow well. It is never economical 

 to proceed blindly in matters which concern health and life. 



Protecting the water of a well. After a well is properly located 

 and dug, and a plentiful supply of safe water obtained, much 

 depends upon the construction and care of the well in order to 

 keep the water safe for all individual and domestic uses. The 

 well should be lined with the best materials, such as specially 

 prepared brick or stone and cement ; the workmanship should be 

 of the best. The lining should be carried above the level of 

 the ground, and a water-tight covering provided to prevent dust, 

 dirt, and other objectionable materials from entering. The 

 purpose of the lining and the covering is to protect the water 

 of the well from possible contamination by surface drainage. 

 The ground surface around the mouth of the well should slope 

 away on all sides so as to carry off all waste water. The ground 

 should be kept clean also, no refuse or decaying vegetable 

 matter being allowed to accumulate on any ground which 

 drains toward the well. 



IV. DAMS 



79. Purposes. Dams are built for many purposes, among 

 which may be cited the impounding and storage of water for 

 private and municipal supply systems, for irrigation, for the 

 generation of power, and for the purpose of diverting a stream 

 from its usual course. Where, for example, the average annual 

 rainfall is comparatively small and inadequate to the needs of 

 a city, as in the case of San Francisco, immense impounding 

 and storage dams have to be built. In the western states of our 

 country there are extensive areas of land which with a sufficient 

 water supply are invaluable for agricultural purposes. Where 

 water is available during a part of the year, the United States 



