SOME REMARKS ON SEWERAGE SYSTEMS. 97 



As a rule, all new sewerage systems are now designed on 

 the separate method, and the old sewers are used for the 

 conveyance of the rainfall into the natural water-courses. 



A good house-to-house water service, laid on at constant 

 pressure from the mains, is in any case absolutely essential 

 to a saccessful sewerage system. No drain, however well 

 laid, will remain clear unless the sewage is thoroughly 

 diluted with water, and this is never certain of being ob- 

 tained except with a constant supply. A house-to-house 

 service will also do away with the danger of contamination 

 of the drinking water, where this is drawn from wells. 



This leads us on to the consideration of some of the de- 

 tails of a water-carried sewerage system. 



The sectional form and dimension of sewers, as well as 

 the materials of which they are constructed, have under- 

 gone important changes from time to time, especially during 

 the last half century. The early sewer works were generally 

 put into the hands of most incompetent workmen, and 

 many sewers were merely old water-courses, into which 

 sewage had already been turned, roughly built up in dry 

 walling, and covered with flat stones. (Several instances of 

 this sort have been found in Bristol.) 



No attempt was made to render them self-cleansing ; and 

 the consequence was that they became " sewers of deposit," 

 into which men had continually to be sent to dig away the 

 accumulated refuse. For this purpose they were made 

 much larger than was absolutely necessary for the work 

 that thej'- had to do. One old sewer in St. Stephen's Street 

 is nearly 6 feet high. 



Rough improvements were gralually made, such as arch- 

 ing over top, building invert, etc.; but it is only within 

 the last half-century, under, I believe, the leadership of 

 Mr. J. Phillipps, that sewers were systematically designed 



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