Polluted Water Can Kill You 225 



enteric diseases. The typhoid, paratyphoid, and dysentery rates 

 have dropped off sharply since measures have been instituted to 

 improve water supphes on both small and large scales. Wide- 

 spread water-borne outbreaks in the United States can be a thing 

 of the past as long as constant vigilance is the watchword. While 

 tvphoid vaccination may attenuate the symptoms of the disease, it 

 is a false notion that a person vaccinated against typhoid is com- 

 pletely protected from the disease. Vaccination is designed to 

 protect the individual from a chance contact with a few of these 

 organisms. The ingestion of large numbers of Salmonella typhosa 

 may still cause typhoid fever. 



TREATMENT OF DRINKING WATER 



The treatment of water to make it potable involves the physical 

 removal of enteric pathogens or their chemical destruction. The 

 use of disinfectants goes back to at least 1897 when Jewell added 

 bleaching powder to the water supply of Adrian, Michigan. Since 

 this date the treatment of public water supplies to make them 

 safe has become widespread. Chlorine gas, liquid chlorine, and 

 various chlorine compounds have been employed since Jewell's 

 early work in the field, and sharp declines in the typhoid rate 

 were recorded upon the introduction of this practice. Rates of 

 twenty deaths or more per hundred thousand population have 

 dropped to less than one death per hundred thousand at the 

 present time. 



The concentration required to satisfactorily disinfect water is 

 usually not over one part of chlorine per million parts of water 

 (abbreviated P.P.M.), with a residual of one tenth to three 

 tenths P.P.M. at distant points throughout the distribution system. 

 Properly chlorinated water ordinarily cannot be detected organo- 

 leptically (by taste or smell) by the average consumer. It should 

 be mentioned that occasional gastro-intestinal outbreaks of non- 

 bacterial origin might arise from filtered and chlorinated water. 

 These outbreaks are probably caused by viruses which are un- 

 harmed by the physical and chemical treatment. Amoebic dysen- 

 tery might conceivably be disseminated through chlorinated water. 



