THE SYDNEY WATER SUPPLY. 227 



construction of the works connected with my proposal, over 

 and above the expenditure which will have to be incurred 

 if it is not adopted, the additional cost expressed in pence 

 per thousand gallons would only amount to a small decimal 

 above one penny per thousand gallons in the year 1922, and 

 this would immediately drop to a little over l/3rd of a 

 penny per thousand gallons in the following year, owing 

 to the stoppage of boosting and pumping the water. 



Thereafter the decline in additional cost would continue 

 until the year 1931-2, when the costs in Columns <f Q" and 

 ^'W are shown to be equal. A saving would then com- 

 mence, which would increase year after year until 1946-7, 

 when the saving would amount to 0.386 of a penny per 

 thousand gallons. 



As the limit of my scheme would then have been reached, 

 that is to say, the pressure tunnels would then be delivering 

 water at their full capacity of 150 millions of gallons per 

 day, any further increase in the daily consumption of water 

 on the higher zones beyond that quantity would, of course, 

 have to be pumped ; but it should not be forgotten that the 

 saving in the cost of pumping 150 millions of gallons daily 

 would continue for ever. 



I have added another column ( ' ' Y " ) showing the excess 

 or deficiency in the cost, expressed in another way, namely, 

 in pounds sterling per annum, which enables one to grasp 

 the magnitude of the saving better than by the previous 

 column. 



It will be seen that in 1922, when the pressure tunnels 

 would be ready to commence duty, the additional cost of 

 my proposal would amount to £274,115. 



Although the yearly additional cost from that time 

 rapidly decreases, it still reaches considerable figures, 

 namely, £419,385 in 1931, on which date the costs of the two 

 Columns "Q" and "W" are shown to be equal. 



