76 WATER 



from far and near, and as it moves from place to place, it 

 carries with it in solution or suspension anything which it 

 can find, whether it be animal, vegetable, or mineral matter. 

 The power of water to gather up matter is so great that 

 the average drinking water contains 20 to 90 grains of solid 

 matter per gallon; that is, if a gallon of ordinary drinking 

 water is left to evaporate, a residue of 20 to 90 grains will be 

 left. (See Laboratory Manual.) As water runs down a hill 



FIG. 37. As water flows over the land, it gathers filth and disease germs. 



slope (Fig. 37), it carries with it the filth gathered from acres 

 of land; carries with it the refuse of stable, barn, and kitchen ; 

 and too often this impure surface water joins the streams which 

 supply our cities. Lakes and rivers which furnish drinking 

 water should be carefully protected from surface draining; 

 that is, from water which has flowed over the land and has 



