UNPOLLUTED WATER

Evening Star, Issue 19274, 12 June 1926, Page 12

UNPOLLUTED WATER

PURE SUPPLY FROM HILLS DISCOLORATION INNOCUOUS FILTRATION FOR CITY RESERVOIRS. Water supplied to the city of Dunedin from the reservoirs on the surrounding hills has been tested, bacteriologically and chemically, and found to be pure. A standard test of purity of a water supply is typhoid. Although cases have been reported in neighboring districts, not a single case has been notified m Dunedin tor many years past. A tumblerful of water drawn from the tap might appear dirty. But the resident can drink it with immunity. Any bacteria would be discovered in little time by the health authorities. The discoloration is unsightly—no more—and perfectly innocuous. Carefully watched are the streams from the watershed to the city’s reservoirs. The streams are vigilantly guarded for pollution from the catchment area to the storage basins. Water containing a high proportion of suspended matter and bacteria of various kinds is greatly improved by being stored in large open reservoirs, such as Dunedin possesses. Most of the solid matter is deposited by gravitation, and a high proportion of the bacteria itself iis carried clown with the sediment. Of the remainder the greater part perishes from lack of sustenance, or is destroyed by the ultraviolet rays of the sun. Calculations show that the water running into the reservoirs of -the city remains in store for over three weeks, and tests have shown that the water used in the houses is quite satisfactory. Dunedin’s reservoirs and their capacities are;—Ross Creek, 50,000,000 gallons ; Southern, 65,000,000; Sullivan’s Dam, 30,000,000; Maori Hill service, 2,750,000; _lloslyn sendee, 768,700; Mornington (Epsilon street) service, 225,000; Brunei street service, 50,600. Ross Creek reservoir has its watershed on .the hills about Flagstaff, and Sullivan’s Dam is fed by streams from Flagstaff and Mount Cargill. Agriculture is not carried out on these watersheds, which is a source of congratulation, as the contamination is made more liable when the streams pass through cultivated land carrying live i stock. The city's biggest reservoir, I Southern, requires jiareful watching. Its catchment area irSilverEtream, and the water' passes through agricultural land.

Tho city’s water is unaltered. Re* presentations have been made in tho past that filtration systems should b© placed in the reservoirs. The reply has been tjjat the prohibitive cost, owing to ibo engineering- difficulties, precluded the work being carried out. No engineer will say that filtration is not necessary. The water might be pure without the installation, but it would be purer if tbe filter was made. The question of filtration has not been seriously considered in Dunedin, but Mr J. G. Alexander (the city engineer) realises that one day tho question will have to be tackled, and tbe engineering difficulties overcome. Tho purest water supply in tho world is claimed for London, which draws its water from the filthy Thames and the Los. Seven reservoirs about the city contain the water. Two are kept filled for three weeks, and the water is then filtered. The oilier five storage tanks are chlorinated —that is, chlorine is placed in the water lor sterilisation, and is drawn off by a chemical process. The water is filtered through sand, and out it goes into the mams as the purest public water in tho world. Many other methods are adopted for purifying the water, Sir Alexander Houston, the export on the Metropolitan Water Board of London, having proposed a number, as well as tho chlorinating system. A case of typhoid fever has not occurred in London within tho past ten years, which illustrates how successful polluted water can be purified. The average daily consumption of water in Dunedin per capita is about seventy-five gallons. In London it is about thirty-nine gallons; in New York, 200; in Berlin, thirty; and in Chicago, 170.