767 



WATER SUPPLY. 



WATER SUPPLY. 



768 



such a course is able to do good, it must, however, be observed, that 

 the water must How with considerable velocity ; aud it would appear 

 that the aeration of the water thus produced constitutes one of the 

 superiorities of river waters over those obtained from ordinary wells ; 

 bee i use the latter are exposed, occasionally, to become stagnant. 

 When a water supply has to be obtained from a great distance, the 

 considerations of the deposition of the earthy salts become of great 

 importance, on account of the effect they are likely to produce upon 

 the delivery of the conducting channels ; and it was precisely because 

 the engineer of the Marseille waterworks, M. de Mxmtricher, feared 

 that the waters of the Durance would choke a reversed syphon that he 

 was led to erect the gigantic aqueduct of Roquefavour. The channel 

 through which any stream is to be led must, it may also be added, be 

 protected from accidental impurities derived from the atmosphere, or 

 from any other source ; and even at the present day, the hydraulic 

 engineer might derive many useful lessons from the practice of the 

 Romans in these details of their aqueducts. They took care, in fact, 

 to cover their channels as far as possible ; to provide ventilating shafts 

 from distance to distance ; and to place drips in the line of the invert, 

 in order to produce small cataracts, with a view to increasing the 

 aeration of the water. 



The objections to the use of ordinary well-waters, on account of their 

 tendency to become stagnant, apply with variable force (according to 

 the quantities considered) to the waters of ponds, of reservoirs, or of 

 lakes; and thertfore they have an important bearing upon the system 

 of the supply to towns, known in England by the name of the " caU-k- 

 ition system." In works of this description, the water, 

 falling upon elevated districts around the town to be supplied, is stored 

 in large artificial reservoirs, in such a manner as to allow the excess of 

 the winters rains to be distributed in the dry season; and evidently 

 these reservoirs must be established so as to ensure the disposal of the 

 maximum quantity for distribution precisely at the season when there 

 would be the least rainfall to renew the water. During the dry season, 

 in fact, the water in the reservoirs cannot be renewed, and it must be 

 exposed to all the deleterious actions which are known to take place in 

 stagnant water from the development of animal and of vegetable life in 

 them, under the influence of light and beat. The purity uf the waters 

 thus stored must, however, depend greatly upon the nature of the 

 surface from whence they flow, upon the nature of the soil of the 

 reservoirs themselves, and upon the exposure, the outline in plan, and 

 the transverse sections of the reservoirs ; for the primary qualities of 

 the water depend on the first of these considerations, and its preserva- 

 tion in a wholesome state depends greatly upon the influence of the 

 I.-itt r in maintaining a surface agitation. The lands which exercise 

 the most deleterious action upon the waters to be impounded are those 

 whieh ore covered by peat, or by agricultural land; or those which are 

 likely to give off mineral or earthy salts in large quantities ; and, 

 therefore, the primary or secondary crystalline rocks and the pure 

 silicious sands are the best adapted for the purpose of forming 

 gathering-grounds. In England, and in most countries where gravi- 

 tation waterworks can be established from reservoirs, such as are above 

 alluded to, it fortunately happens that the gathering-grounds occur in 

 the hilly districts of the primary formations; but in India, and in 

 1 alluvial plains, it is often necessary to store the excessive 

 rainfall of the wet season in tanks, for consumption during the dry 

 season, because tlje superficial water-courses cease to yield water, and 

 there are no perennial springs in such districts. The waters so tftored 

 must, under these circumstances, be filtered, or treated in some way, 

 in order to counteract their otherwise deleterious effects upon the 

 human frame ; the great difficulty, however, arising from the tempe- 

 rature to which they are raised by the sun's action upon their surface. 



It would appear, after all, that the waters which unite the greater 

 number of favourable qualities for a town supply are those which flow 

 from deep-seated springs, or from the insoluble clay slates, crystalline 

 limestones, or are obtained by continuous pumping from wells sunk in 

 the pure silicious strata, &c. It is not often that these wells yield water 

 in sufficient quantities for a town supply ; and there is always a danger 

 of their being interfered with by the operations of neighbours, or by 

 injurious infiltrations from cesspools or dead wells. The history of the 

 Artesian wells round London, of those at Tours and Paris, aud of the 

 deep wells in the new red-sandstone at Liverpool, proves that there are 

 serious objections to allowing the supply of a large population to 

 depend on .-ources so uncertain, and so easily diverted, as these deep- 

 seated springs evidently are. In no country in Europe is there any 

 legislation creating a right of property in underground waters ; for 

 law-makers have not hitherto been geologists, and they have openly 

 avowed their ignorance of the principles which regulate the flow of 

 deep-seated springs. It thus happens that the inhabitants of large 

 towns are compelled, practically, to resort for their water supply either 

 to rivers or superficial wuter-courses, or to create reservoirs upon either 

 the gravitation or the tank system, to impound the rainfall of the 

 wet seasons. 



In the previous portion of this article it was stated that the quantity 

 of water to be distributed in a town was usually calculated at the rate 

 of 40 gallons per individual per day ; but evidently local circumstances 

 may atlect this rate of consumption to a very serious extent. It is 

 more than questionable whether even the most luxurious ] 

 require absolutely a greater quantity than (i gallons' per day for their 



own immediate consumption ; and if the latter be carried to 1 gallons 

 per day, it would suffice with proper care for any real demands. In 

 calculating for a town supply, it is necessary, however, to allow for the 

 consumption by trades usiug large quantities of water, and for muni- 

 cipal purposes, such as street-watering, flushing sewers, extinction of 

 fires, &c. ; and, in order to cover these demands, it was considered, so 

 long as the old-fashioned intermittent supply existed, that an allowance 

 of 20 gallons per head per day would be sufficient. The introduction 

 of the constant-delivery system has of late years tended singularly to 

 increase the quantity of water distributed, and indeed the waste of 

 water which thus takes place is at times so great that it almost assumes 

 the importance of a public calamity. In London, where the inter- 

 mittent supply still prevails, the consumption of water is now not less 

 than at the rate of 40 gallons per head per day on the average ; in 

 Croydon, at Boston, New York, &c,, the rate under the constant 

 delivery has been 80, 100, and even sometimes 500 gallons per head 

 per day. No doubt a great part of this waste could be prevented, and 

 it would never be allowed to exist if the water supply of towns were 

 left in the hands of private companies ; but the tendency of the a?e is 

 certainly to withdraw municipal services from the control of speculative 

 adventurers, and it therefore becomes important to direct attention to 

 the eventual danger ari-ing from the waste which seems to be inherently 

 attached to the modern system of distribution. 



Whatever may be assumed to be the normal rate of consumption 

 by the inhabitants of a town, it mnst be observed that, in the summer 

 months, that is to say, in June, July, August, and September, the 

 average consumption per individual per day increases in about the ratio 

 of 10 per cent, upon the ordinary average ; whilst in December, 

 January, and February it is about as much below the same average. 

 In designing gravitation-works, especially, this becomes an important 

 consideration ; for the consumption actually increases when the supply 

 decreases, and the dimensions of the reservoirs must be calculated of 

 sufficient size to meet the demand of the season which is the most 

 unfavourable. The compensations to be given to the ancient poss ssors 

 of water privileges must also be taken into account in designing any 

 new water-works, especially in the case of gravitation-works, which 

 interfere more with the natural hydrographical conditions of a district 

 than ordinary pumpiug-works do j and the loss of water by evaporation, 

 from the icservoirs in hot weather requires also to be allowed for. In 

 most countries of Southern Europe, it is to be observed, moreover, 

 that the rate of personal consumption of water, so to speak, is much 

 less than the rate prevailing in the north, but that the quantity of 

 water poured down the channels, or used in the monumental fountains, 

 or in other contrivances for cooling and refreshing the air, is, on the 

 contrary, very much greater. Thus, in Paris, it is stated officially that 

 the supply of water takes place at the average rate of 13} gallons per 

 head per day ; but, in fact, the water is sold by the pail, aud in no 

 house in Paris is there a supply (in 1861) to the second floor, and 

 nearly all the water which is brought into the city is poured into the 

 street kennels or is employed in the fountains. All these details of 

 the application of a town supply must, therefore, be carefully examined, 

 and allowed for, in selecting the source and mode of distribution ; for 

 it must be evident that every particular climate, and every phase of 

 civilisation, requires to be treated upon its own special principles. 



The quantity and the quality of the water supply being determined, 

 a very important question arises, as to whether it should be obtained, 

 at a great original outlay, under such conditions as to allow the water 

 to flow to the place of distribution, by gravitation ; or whether it 

 should be obtained by means of pumping-machinery, at a smaller 

 original outlay, but at a greater annual expense for working. This 

 question is one which it is impossible to decide d priori, because it 

 must be so materially affected by local considerations as to render it 

 dangerous to lay down any absolute rules in the matter. But it must 

 be evident that, wherever it is possible, as it was in the case of ancient 

 Rome, to lead into a town streams of water rising at a natural elevation 

 above the proposed points of distribution, there must be an eventual 

 economy in so doing over the cost of another system by whieh the 

 water would be raised from even a nearer point by the aid of a compli- 

 cated piece of machinery. The Romans, who were able to concentrate 

 upon any work they undertook the resources of the known civilised 

 world, adopted the former system ; and the highly-centralised govern- 

 ment of modern Europe evidently prefer it, for the French are about 

 to incur an enormous expense in order to lead to Paris, by gravitation, 

 some springs which rise at a great distance from that town. In 

 England and in America, however, where individual enterprise is so 

 much more active, the tendency is to resort to sources of supply which 

 admit of the application of machinery at a small primary outlay ; and, 

 in fact, the choice between the two systems must greatly depend upon 

 the power of commanding capital, aud upon the balance of rnotivejj 

 which might lead to imposing a burden upon the present generation 

 for the sake of its successors. In either case, the works required for 

 the filtration, storeage, and distribution of the waters are the same ; 

 the only difference consists in the mode of leading the water to the 

 point I'rom whence the distribution is to take place. 



Even in gravitation works there are various methods of solving this 

 question, for the water may be led either in closed pipes or in open or in 

 covered conduiU. Open conduits may be resorted to when the district 

 they traverse is not likely to furnish ;uiy elements of a nature to alter 



