340 THE WATER PROBLEM OF A LARGE CITY 



pumping engine working at full speed every second of the day 

 and night would be able to supply the town with the necessary 

 amount of water. When, however, we consider the actual 

 height to which the water is raised above the pumping station, 

 and the extra pumping which must be done in order to balance 

 the frictional loss, it is easy to understand that in actual prac- 

 tice a much more powerful engine would be needed. 



In many large cities there is no one single pumping station 

 which supplies all parts of the city, but several pumping 

 stations are scattered throughout the municipality, each of 

 which supplies a restricted territory. 



Water and its dangers. We need an abundance of pure 

 drinking water, but the water of lakes and streams is seldom 

 pure. This is because running water picks up animal and 

 vegetable matter and carries it along in solution and suspen- 

 sion. 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. 

 As water runs down a slope it carries with it the filth gathered 

 from acres of land, carries with it the refuse of stable, barn, and 

 kitchen. 



Too often this impure water finds its way into the streams 

 that supply our cities (Fig. 209). One winter in Plymouth, 

 Pa., excreta from a typhoid patient was thrown on a snow- 

 bank. With the first warm days of spring, the snow melted 

 and ran down into one of the city's reservoirs, carrying with it 

 excreta on which typhoid germs were living. Within a few 

 weeks over 1000 of the citizens who used this reservoir were ill 

 with typhoid fever. 



All lakes and rivers which furnish drinking water should 

 be carefully protected from surface drainage; that is, from 

 water which has flowed over the land and has accumulated 



