THE CHRISTCHURCH ARTESIANS AND THE CITY WATER SUPPLY.

Star (Christchurch), Issue 17352, 17 May 1924, Page 8

THE CHRISTCHURCH ARTESIANS AND THE CITY WATER SUPPLY.

BY

CHAS. CHILTON

(Rector and Professor of Biology, Canterbury College. N.Z.) * XXIX. RESERVOIR OR NO RESERVOIR? The questions about (lie reservoir, -whether (if there were to lie one) it should be open or covered and whether it was not nn™l e n H d ° 7'":°"} a res . ervoir b - v llsin « a -water tower or bv pumping djrec-t into the mains, were the cause of a large part of the correspondence and discussion that centred around the Citv Council s proposals m 1907, and though they were settled at the time by the erection of a reservoir, afterwards covered in, on the Cashmere Hills, the points raised are of much importance in connection with the proposals recently made for the extension of the city s supply. The criticism that the pure artesian water might become contaminated if pumped into an open reservoiir led the council to ha\-e examinations made by the bacteriologist ' Public Health Department, though apparentlv the desiratnlitv ot doing tins had not previously been thought of. The results of the examination, as reported bv the Public Health Oil leer a few days before the poll, were that a sample of the ■«ator from the Sydenham supply (for which a water tower was used) contained thirty microbes per cubic centimetre, equivalent to about 100 in a tenspoonful of water, and that a sample of water from the Lyttelton supply (for which an open reserve had been used for many years) contained .160 microbes per cubic centimetre of about 1830 in a teaspoonful. These facts were "f“ r ' e . d to b' o , City Council by the Public Health Officer on June -2, 190/, and though, as lie said, they showed that the Svdenham water contained a low number of microbes thev did not seem to the critics to tell in favour of an open reservoir. Fuller investigations were made on July 18, 1907, after the poll had been carried, and were reported to the council on August 12, 1907 Die observations were also made on the Svdenham water supply. For the purpose arrangements had been made to have one ot the reservoirs emptied so that a sample could be obtained direct from the artesian pipe; samples were also taken from the deposit at the bottom of the tank and from the surface of the lull tank, the water from the well showed only- twentv organisms per cubic centimetre, that from the top of the full tank showed eighty- per c.c., and that from the bottom of the almost empty tank 135 per c.c. Cultures made from the water at the bottom of the tank showed no growth yvhen kept at 37 degrees centigrade, thus indicating a freedom from any pathogenic germs, for “ most of the ordinary organisms found in water did not grow at that temperature, and it yvas safe to conclude that the 135 found in cultures groyvn at lower temperatures consisted wholly of harmless germs, since all those giving rise to water-borne diseases could grow at 37 degrees.” There was no further report on the Lyttelton water, and while the results reported showed that the Sydenham water was well within the limits* allowed for a drinking water, it showed also that the water direct from the yvell yvas almost free from organisms and that more-were found even in a small reservoir such as the tank on the Sy-denliam yvater tower, the conclusion naturally to be drawn seeming to he that the niore directlv the water was pumped into the mains from the artesian the better. No further bacteriological examinations of the Christchurch waters have been made by the council from 190/ up to the present year and then they were not made till after the proposals for the extension of the supply had been rejected bv the citizens in January last. With regard to the proposals for pumping direct into the mains the City- Council’s engineers in 1907 admitted that “ other things being equal, the more directly- the water is passed from the artesian well to the consumer the better for its purity, the inference being that pumping direct into the mains is preferable to pumping into a reservoir, whether covered or not. A scheme involving this principle was accepted by the council in 1902.” Owing to the difficulty of interference with existing wells, shown by the result of pumping on the well in Market Square as alreadyrelated, the scheme had been rejected when placed before the citizens. The engineers therefore considered it hopeless to approach the ratepayers again with any scheme involving the risk of interference with the wells in town. This was one of the reasons for going to Cashmere for the supply of water for the city. In view of subsequent events it is greatly to he regretted that before doing so the engineers did not try' to eliminate the results of interference by obtaining the supply from the deeper strata not tapped at that time by private citizens. They further pointed out in the report to the Mayor on June 22, 1907, that: “ In any scheme involving pumping direct into the mains the pumping plant must have sufficient capacity to supply- water at the requisite pressure and in sufficient capacity to cope with a large fire, in addition to the ordinary- draught on the mains .” and that a “ sump ” or tank from which to pump was therefore necsesary- and that this would have to be just as large as the elevated reservoir on the Port Hills. At the public meeting held on June 24. 1907, to consider objections that had been raised to the council’s proposals the engineer’s reasons for not pumping direct into the mains were repeated and it was said to be a most inefficient system, adopted only- when no better system could be obtained. Accordingly the city went to Cashmere for its yvater supply- and built the reservoir on the Port Hills. It is rather a strange comment on this past history that in the little handbook issued by- the City Council for the present year the account of the city- water supply, after giving the number and position of the wells and a description of the pumping machinery, adds:—“The yvater is pumped directly into the main.”

In reply to the suggestion that a water tower might be used instead of the reservoir, as yvas actually being done at Sydenham, the engineers stated in the report to the Mayor: “ Water towers are merely reservoirs on stands and are only resorted to in the absence of solid foundations, such as an adjacent hill, and when of sufficient capacity- and elevation for fire extinction purposes are very costly- contrivances, not to mention the possibility of the whole affair being shaken down by an earthquake.” This was apparently another of the reasons for placing the pumping station at Cashmere with the reservoir on the adjacent hill. In reply- to the engineers it was at once asked why they had in their scheme recommended water towers for the Linwood and St Albans Wards and was it not true that large mains, such as the one that would be required to bring the yvater from Cashmere to the city, were as liable to be damaged by earthquakes as water lowers were. That yvas in 1907 —the water tower at Sydenham is still standing, but in the interval the main from the Cashmere station has twice been broken, not, indeed, from an earthquake, but from other causes quite as likely to occur in Christchurch as earthquakes. (The next article will appear on Wednesday, May 21, 1924.)