Polluted Water Can Kill You 227 



chemical to remain in the well overnight, and then pump out the 

 water until the odor of chlorine disappears. A bacteriological ex- 

 amination will usually show that such treated water is now ready 

 to be used for drinking puiposes. 



Persons engaged in testing small water supplies are frequently 

 confronted with requests for information as to what should be 

 done when small animals are found in the well. Had the supply 

 been properly covered, such animals as rabbits, skunks, cats, mice, 

 etc., would not be able to get into the well. The presence of these 

 animals is often not detected until advanced decomposition has set 

 in and strong tastes and odors are noticed in the water. The 

 usual advice for such conditions is to remove the animal, or its 

 remains, and to chlorinate the water as described above. Such 

 chemical treatment will leave the water with a good taste and the 

 bulk of the bacteria generated during the decomposition are 

 usually eliminated. 



RESERVOIRS AND OTHER LARGE BODIES OF WATER 



Large bodies of water contain appreciable quantities of organic 

 debris, and upon standing for long periods of time, much of fhe 

 undesirable material will settle out. Microorganisms are carried 

 down with these particles, and bacterial numbers are then ma- 

 terially reduced through natural antagonisms. To speed up this 

 process, various chemicals can be added to the water as it is stored 

 in settling tanks. These chemicals (including iron and aluminum 

 sulfates) form a flaky precipitate and carry a great deal of 

 suspended matter with them to the bottom of the tanks. 



While a high percentage of organisms may be removed from 

 water in these chambers, it has been found desirable to follow 

 sedimentation with filtration through sand. Filtration dates to 

 1829 when the river water of London was passed throu2;h sand to 

 remove undesirable matter. Even though the germ theory of 

 disease had not yet been established, records reveal that filtration 

 appeared to reduce the incidence of intestinal upsets among those 

 who drank the treated water. 



One of the classics recorded in microbiology is the famous case 



