XLVI. J. M. SMAIL, 



Fortunately, so far, Providence is bountiful in giving the 

 citizens of Sydney one of the best natural water supplies 

 in the world, which only needs the treatment of Nature's 

 laboratory on its course to the metropolis, added to mechani- 

 cal straining prior to distribution. How long this state of 

 things will last depends in a great measure on the citizens 

 themselves in preserving the natural purity and prevention 

 of pollution. The amount of money spent in Europe and 

 America in artificial purification is enormous; this, how- 

 ever, is the result of centuries. In this State the source 

 of supply is practically in its virgin state — that it should 

 be so kept is a duty which devolves upon every citizen. 



It is a very difficult matter to obtain reliable data as to 

 the cost of maintaining slow sand filters, the yearly charges 

 being, as a rule, mixed up with other maintenance charges. 

 I hope to be able to shortly obtain other information on this 

 bead which will be of use in question with relative merits 

 of the two systems. 



Appendix. 



1. In judging the quality of a filtered surface water, the 

 following points should be specially observed : — (a) The 

 operation of a filter is to be regarded as satisfactory when 

 the filtrate contains the smallest possible number of 

 bacteria, not exceeding the number which practical experi- 

 ence has shown to be attainable with good filtration at the 

 work in question. In those cases where there are no pre- 

 vious records showing the possibilities of the works and 

 the influence of the local conditions, especially the character 

 of the raw water, and until such information is obtained it 

 is to be taken as the rule that a satisfactory filtration shall 

 never yield an effluent with more than about 100 bacteria 

 per cubic centimetre, (b) The filtrate must be as clear as 

 possible, and in regard to colour, taste, temperature, and 

 chemical composition, must be no worse than the raw water. 





