206 



THE WORK OF RUNNING WATER 



by filtering through thick beds of sand and gravel. Finally 

 small amounts of chemicals are added to kill the harmful 



SSTSS 



FIG. 82. DIAGRAM SHOWING ST. Louis WATER PURIFYING PROCESS 

 The arrows show the course of the water through the plant. 



bacteria, and the pure water is aerated and forced through 

 the mains. None of the chemicals used makes the water 

 harmful to drink or unpalatable to the taste 



SUMMARY 



When rain falls, some of it evaporates ; some flows away 

 on the surface of the land; some sinks into the ground, to 

 return as springs or wells. The water which flows along the 

 surface has a great effect upon the land. It forms the 

 little streams which remove the surface water, the huge 

 rivers which drain the country and form great arteries of 

 trade, and the beautiful lake-reservoirs which hold back 

 floods and offer easy transportation to ships. 



