SOURCES OF WATER SUPPLY.

New Zealand Herald, Volume LXV, Issue 19889, 7 March 1928, Page 10

SOURCES OF WATER SUPPLY.

The criticism by the Mayor of Mount Eden of the city engineer's provisional report on the Hunua ranges as a future source of water supply is remarkable for the complete absence of any substantial basis for the comparisons he makes. Mr. Bush has approximately estimated the cost of the Mangatawhiri and Mangatangi development at £2,700,000, which Mr. Potter says "is more than enough to obtain water from Arapuni, where the supply would be unlimited." Unless that statement is simply designed to foster ill-informed prejudice, it must mean that a similar quantity of water could be got from Arapuni as Mr. Bush proposes to obtain from the Hunua streams for the same capital cost. If the latter interpretation is proposed, it is surely Mr. Potter's responsibility to substantiate his estimate. The Hunua development will be 38 miles from the city; Arapuni at least 100 miles. Mr. Potter says the cost of mains is £14,000 a mile and might argue that the additional distance could be covered by the allocation of £960,000 for the two dams in Mr. Bush's estimates. But how much water will be carried by a main costing £14,000 a mile? The figure of £2,700,000 quoted by Mr. Potter represents the whole cost of a development, to be undertaken in two stages, in which the cost of mains appears to be about £35,000 a mile. It will deliver 23,000.000 gallons daily. Does Mr. Potter seriously suggest that, an equivalent quantity of water can be pumped from the' unlimited storage at Arapuni and delivered to the city as cheaply as from the Hunua ranges'? Such a conclusion is a direct contradiction of the Water Commission's report. It calculated the cost of a supply of 11,000,000 gallons a day from Mangatawhiri, Mercer, Arapuni and Lake Taupo. The first would cost 7.54 d per thousand gallons, the second 7.7 d; while Arapuni water would cost 14.7 d and the Lake Taupo scheme 19d, Moreover, the complete development of the Hunua project would bring the cost of 23,000,000 gallons down to 5.7 d, while larger supplies from any of the other sources would cost approximately the same rate per thousand gallons as the first 11,000,000 gallons. In the face of such calculations, it is misleading to discuss the subject in terms of the quantity of water at any particular point. To say tha£ enough flows over the Arapuni spillway in ten minutes to supply the whole of Auckland, as a Mount Eden councillor observed, does not demonstrate its economy as a source of water for Auckland. It has about as much relation to the matter as a calculation of the quantity of material in Mount Eden would have upon the proposal to build a bridge across the harbour*