764 KEPORT— 1903. 



Water Supply. 



To everyone a plentiful supply of good water is not only a luxurj-, but almost 

 a necessity of existence, yet how few even amongst the more intelligent of the 

 millions who are accustomed to find such a supply ready to hand at the nearest 

 tap have more than a very imperfect notion of the works that have to be con- 

 structed to obtain it, or the daily care and attention given to secure and maintain 

 its purity, to ensure its elllcient distribution, and to prevent its waste by careless, 

 ignorant, or reckless consumers. It may therefore not bo out of place that when 

 the chair of this Section of the British vVssociation happens, as now, to be occupied 

 by one whose professional life has been largely associated with waterworks under- 

 takings, he should address you on that subject, and endeavour briefly to direct 

 attention to some of the main features of waterworks construction and manage- 

 ment. In following that course I shall, however, necessarily have to describe 

 what is already well-known to at least a portion of my audience, on whose indul- 

 gence I must therefore rely. 



Water supplies may be divided into two main classes, namely, 'Gravitation' 

 and ' Pumping.' In some instances a combination of gravitation and pumping is 

 resorted to, especially in those cases in which the more elevated portions of the 

 district to be supplied are situate above the gravitation level. In selecting a 

 suitable source of supply the main points for consideration are the quantitj/ and 

 the quality of the water. The quantity should be such as will not only suffice to 

 meet the requirements throughout the most protracted periods of drought and 

 frost of the existing population to be served, but should provide for the probable 

 growth of that population during a reasonable number of years to come. The 

 quality of the water selected should be the best that can be obtained, having due 

 regard to considerations of expense. The question of the altitude being sufficient 

 to permit of a supply by gravitation is of far less moment than those of quantity 

 and quality, because the difference in cost between water derived by gravitation 

 and that obtained by pumping is, in the United Kingdom, less than is generally 

 supposed ; indeed, contrary to popular belief, gravitation water is frequently more 

 costly than pumped water, owing to the much greater capital outlay usually 

 incurred in the construction of the works for storing and conveying it. 



Gravitation works may be divided into three classes, namely, those in which 

 water is taken directly from a spring or stream without storage, those in which it 

 is taken from a natural lake, in which case the surface level of the water is usually 

 raised so as to increase the capacity of the lake as at Thirlmere, and those more 

 numerous cases in Avhich the water of a spring is impounded in an artificial 

 reservoir generally formed by the construction of an earthen or masonry dam 

 across the valley along which flows the stream to be taken. 



In the more populated portions of England it is becoming more and more diffi- 

 cult to find an unappropriated gathering ground available as a source of water 

 su])ply. The gathering ground, or drainage area as it is frequently termed, should 

 either be free Irom human habitations and otlier sources of possible pollution, or 

 any pollution arising tlierefrom should be cap.able of being efficiently disposed of 

 by removal from the area of the gathering ground or otherwise. 



The gathering ground must also possess a site suitable for the formation of an 

 imjjounding reservoir. AVhon this lias been selected it next becomes necessary to 

 ascertain the amount of the available rainfall, as recorded by rain-gauges situate 

 in the drainage area or its immediate vicinity, or where these are not available, as 

 deduced from the returns obtained from more distant rain-gauges, care being 

 always taken that some at least of the gauges have been observed for a sufficient 

 number of years to enable the true average rainfall to be determined. To store 

 the whole of the water flowing from a gathering ground during a cycle of wet 

 years in order to utilise it during a cycle of dry years would entail the construction 

 of reservoirs of enormous capacity, at a cost incommensurate with the object to be 

 attained ; it is therefore customary to make them of such size as to enable the 

 supply to be maintained without risk of failure throughout the three driest con- 

 secutive years, the mean annual rainfall of which years generally amounts to 



