SYMPOSIUM OX SANITATION 53 



the discharge of all deleterious matter into streams. It is only 

 reasonable to require that the pollution of streams be main- 

 tained at less than a certain fixed maximum and this permis- 

 sible maximum pollution must vary according to the character 

 of the stream, the population along the banks of the stream 

 and the uses to which the waters of the stream are placed. 

 The extent of pollution that is reasonably permissible in 

 streams will be discussed somewhat in detail under the head- 

 ings, ''Streams Used for Public Water Supplies." "Streams 

 Used for Recreation Purposes." "Fish and Shell Fish," "Dis- 

 charge of Manufacturing ^^'astes into Streams." and "Legal 

 Control Over Stream Pollution." 



Streams Used as Sources of Public Water Supplies 



Since streams in the ordinary course of events must re- 

 ceive more or less contamination, it follows that public water 

 supplies drawn from surface streams must of necessitv be 

 polluted and should not be delivered to the consumers unless 

 the water is first adecjuately purified. One exception may be 

 made to this general rule, namely, in the case of water sup- 

 plies derived from streams draining comparatively small water 

 sheds. In such cases it is sometimes feasible for the water- 

 supply authorities to own the entire watershed and control 

 it in such manner as to make cantamination of the water 

 courses impossible- But in general we have this question to 

 contend with — how much pollution may be permitted to enter 

 a stream before the water thereof is polluted to a point be- 

 yond redemption by water purification methods? This is a 

 question that taxes the greatest ingenuity of sanitary experts 

 and it is always necessary for any specific problem to be 

 considered on its particular merits in order to obtain what is 

 the best and most economical solution. 



Merely to indicate the wide range of conditions that are 

 met in actual practice, we have on the one hand a water purifi- 

 cation plant constructed for the purpose of purifying crude 

 though rather weak sewage at the Chicago stock yards. It 

 was claimed that the results obtained at this plant were satis- 

 factory when judged by analytical standards and by the 

 safety of the water for human consumption. Even though it 

 is . possible to transform such a filthy liquid into drinking 

 water, the esthetic sense of the community rebels and it is not 

 probable that water once so highly polluted, even with most 

 thorough purification, will ever be considered as acceptable 

 water for public water supplies. At the other extreme is the 

 community which derives its supply from a clear mountain 

 stream, possibly having its source in large springs yielding a 

 water of unquestioned purity. In such a case there would 

 seem to be but trifling danger, and authorities might be tempt- 



