THE RELATION OF SEWAGE FLO\\' TO WATER 



SUPPLY. 



By WTLr.iA]\T John Davenport. 



It will be noticed in the accompanying diagram* that the 

 sewage flow is approximately 60% of the water consumed. This 

 is to be accounted for by the fact that the town is not completely 

 reticulated with sewers. The balance of the water consumed is 

 at present disposed of by French drains or thrown on the soil, etc. 

 By examining the diagram it will be noticed that the water con- 

 sumption is at its lowest whilst the sewage flow is within 

 i| million gallons of its absolute maximum per month — during 

 the month of July — or an absolute maximum percentage of water 

 consumed reaching the sewers of 74.6. During August, although 

 the water supplied has increased by five million gallons, the quan- 

 tity reaching the sewers is less by six millions of gallons. As 

 gardens are now being put in order, etc.. it indicates that five 



70 



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Jan Feb Mar Apl Mav Ju.n Jly Aun Sep Oct No^ Dec 



million gallons of water liave Ix-cn used for irrigation purposes, 

 in addition to six millions that have been first used for household 

 purposes. 



September is a dry month, and it will lie seen that a further 

 seven million gallons of water was consumed, coupled with a drop 

 of three millions in the sewage outflow. Tliis gives twelve 

 million gallons of water used for garden purposes, plus nine 

 million gallons that have first been used for household purposes. 



October sees another six million gallons consumed, or a total 

 above July of thirty-five million gallons. It will be observed 

 that the sewage discharge lias increased to nearly the July quan- 

 titv, from which it can be inferred that, as rain has fallen, the 

 inhabitants are less thrifty, and are content to allow practically 



* A comparison of the water consumed in Johannesburg during 1912, 

 with the flow of sewage as affected by the rainfall. 



