DISTILLING WATER

Sun (Auckland), Volume III, Issue 786, 5 October 1929, Page 31

DISTILLING WATER

DROUGHT SUGGESTIONS IN ENGLAND DRiNKING THE SEA Among the solutions suggested lor the water shortage owing to the present drought in England is that of a naval engineer-captain, who has suggested in a letter published in the “Daily Telegraph’* recently that distilling plants should be run up in order that’ we may avail ourselves of the water in the sea as well as in our lakes and rivers. The Navy, he pointed out, distils its own fresh water at sea. At Aden all the water used, with a trifling and occasional exception in the rain-water tanks, comes from the same source, while on land the water supply during the siege of Ladysmith was sustained by disilling impure water. The suggestion was put by a representative of “The Observer’* to the London Metropolitan Water Board, "hose spokesman replied that distillation was not at present a method of water-supply favoured by the board, and was indeed for the time being unnecessary. The Government chemist, Sir Robert Robertson, who is chairman of the Water Pollution Research Board, admitted that the Project was theoretically possible, but declared that it was practically too expensive in money and in fuel. “The Plant er ployed by ships at sea is a special plant made to deal with a necessary risk. A plant sufficient to deal with the needs of even a small seaport would have to be built on an entirely different scale, and the prospect of providing the supply of inland towns from the sea is much too complicated a question to be soluble even by a great number of such Plants. Most of the fresh water we now use is obtained by purifying polluted water. Distillation, which is an entirely different method, implies the Provision of immense quantities of •uel. such as we cannot afford. No, 1 think we shall have to content our•*lves with praying for rain.”

Mr. W. T. Burgess, tlie analyst, who is consulting chemist to the greater part of the British water world, agreed. “You could,” he said, "in theory extract the salt which forms 3 per cent, of sea water by chemical means, for though common salt (sodium chloride) is among the most soluble of compounds, certain salts, such as the silver nitrates which photographers use, can be employed as re-agents to drive it out. But consider the expense of these re agents and the limited supply which we have, and it is clear that even distillation would be more practicable. And this perhaps, even if our friends the engineers could make the process a little cheaper, would not wholly satisfy the consumer, who does not dud distilled water altogether palatable to the taste. Salt water undistilled is of course not drinkable at all, nor Is it any use for agriculture or gardening upon the land, but it could very easily be used for bathwater, if those who used it were not too keen on getting a lather, though even here there would be difficulties in pumping it inland.” One of the principal firms of waterengineers, whose distillation plant is actually among those employed to give Aden its exemplary distilled water supply, was next consulted. “It is just a question of the amounts needed,” said the manager of the distilling branch. "For ships at sea we have only to supply plants capable of giving a ton or two of fresh water a day. At Aden (and we have cwo or three dozen plants established in the Red Sea) we have no distilling apparatus which need give more than 40 tons. Our biggest plant of the kind is in Egypt, and this supplies 350 tons of fresh water a day—about 80,000 gallons. This costs about £IO,OOO and takes about six months to build. Then there are the running costs. You start by heating up the water jacket of steam, and this takes about a pound of coal to every eight pounds of steam. Then each pound of steam will evaporate 45 pounds of fresh water. That is to say a pound of coal will produce between three and four gallons of fresh water. Y T ou may calculate the cost of the coal required; three or four gallons a head would not go very far in meeting the needs of even one person for a day, nor would even our own biggest plants supply the needs of many thousand people.” _

How great these needs are was explained by Mr. A. T. Hobbs, the Secre- . tary of the Institution of Water ; engineers. “The minimum supply of , water which is used by persons who have some difficulty in obtaining it, and have to go to wells or outside taps, has been calculated at six or ■ eight gallons a head a day. If you have taps and water-closets and baths the average consumption goes up rap- ’ idly, and I may give you the most recent figures for some typical towns. Sunderland, where the consumption is unusually low, takes an average of 20.03 gallons a head a day; Manchester, 36.4; London, 36.5. This is about the average for England, though Plymouth. is as high as 52 gallons. In Scotland for some reason the consumption of water is greater in proportion. Aberdeen’s 47 gallons a head each person is low. Sterling’s 63 gallons is average, while the town of Duone goes up as far as 125 gallons as the average consumption of the ordinary person all the year round. This is about the same as the results obtained by tests at a large Edinhugh Hotel, where most of the guests had a bath each day, so you may take it that the inhabitants of Duone are perhaps exceptionally clean. "I need not, I think, stress more than is already being done, the possibility, and indeed necessity, of reducing the average consumption of water by economy. We find that our statistics of consumption go up every year, owing to the installation of baths in all the new houes built, and this is all to the good as a rule, but in the present crisis it adds to the difficulties of the water authorities. “Distillation as an emergency measure is, I am sure, a fantastic proposal. , Suppose for a moment you could erect sufficient plants on the seashore, and provide sufficient fuel. (London alone would require at least 30,000 tons of coal a day!) You would still have to provide England with an entirely new system of canals, or else an enormous pumping system, for the distribution of your water before or after distillation. Water now comes down from the hills, and each of the big cities has provided ■ conduits for itself, and for neighbours who tap its supplies. Manchester in normal times sells eight million gal- , lons of water to neighbouring centres, Sheffield four million, Glasgow two million, Halifax three million. As an emergency measure many big towns

are borrowing water from one another. But we have here a system of conducting fresh water from lakes and rivers, not a system of bringing water up from the sea.”