310 



THK WATRIl-SrPPLY OF TOWNS IN THK TROPICS 



Extrncts from 

 final Report to 

 the Sudan 

 Government 



"1. If the Ijods of chiy, sopamting the polluted water in these strata from the deeper water, were or 

 were uot impermeable. 



" 2. If the methods of cutting off the upper strata by means of iron tulics and ocmcut rings were or 

 were not adequate. 



"For this purpose one maintained that continuous pumping trials, extending over a period of 21 consecutive 

 tlays, were essential so that a mH.ximum depression might be obtained in the wells, which in this way would 

 be subjected to a trial more severe than any they were likely to undergo when being pumped on for the 

 town supply. 



" The condition of the wells which were tested in groups of two was as follows: — 



" No. 1. Depth, 100 metres. Upjxir strata cut off to a depth of GoJ metres. 



"No. 5. Depth, 112 metres. Upper strata cut off to a depth of C9J metres. Combined yield 

 18,000 gallons per hour. 



" No. 6. Depth, 75 metres. Upper strata cut off to a depth of 53-82 metres. 



" No. 7. Depth, 176 metres. Upper strata cut off to a depth of 724 metres. Combined yield 

 21,000 gallons per hour." 



It would take up too much space to give the results in detail. Their general consideration, as stated in 

 the report, will suffice, but the tables in the Appendix will be found useful for reference (ride paijes 314, 315 and 31G). 



" So far as Wells No. 1 and No. 7 go, these do not call for any lengthy discussion. A glance at the attached 

 table will show that in both cases, and especially in No. 7, the colony count has almost throughout been 

 uniformly low and compatible with that obtainable from true deep wells containing water free from bacterial 

 impurity. On three oc<^'isions, March 18, 21 and 22, on which the count has exceeded 50 colonies per 1 c.c., 

 the results c!»n probably Ije adeiiuately explained by the hypothesis that some of the foul condensation 

 water from the air-pipe line was forced into the well. Persoually, I am almost certain that this did occur 

 on several occasions, and accounted for the greater number of colonies.* Excluding these abnormal counts, 

 the average colony count for both wells works out at 5-8 per 1 c.c. 



"Further, and this is of greater, indeed of paramount importance, B. coli has not once been found in either 

 of these waters in the quantities (100 c.c. and under) examined, nor has any other objectionable organism 

 been found. 



" Hence, al the present time, the water of these two wells may be passed as a good drinking water, the 

 only possible objection to it being that it is not well aerated and that it is warm, both faults which can be 

 readily remedied. 



"The slight odour of sulphuretted hydrogen in No. 7 Well-water does not call for any special criticism. 



"Taking next Well No. 6, we find that its water closely resembles that found in No. 1 with a single 

 exception. For the greater part of the trials there was present in it an organism closely allied to, 

 if not identical with, B. protctis fluorcscens.^ It is necessary to consider the precise significance of an 

 organism of this type in deep well-water. Its morphology and cultural characteristics will be found 

 discussed in the Appendix, page 317, and, as the same organism was present in No. 5, the remarks here made will 

 apply, so far as this matter is concerned, equally to that well-water. As has been pointed out B. proteus 

 fluorescent is an organism capable of developiug and multiplying in bile-salt media, and it is well known that 

 the majority of organisms which do so are to be regarded with suspicion. Moreover, this is the very bacillus 

 which Jaeger'" and others have claimed, apparently with some reason, as the cause of infective jaundice 

 (Weil's Disease), a condition not uncommon in Egypt and elsewhere in tropical or sub-tropical countries. It 

 was, however, in Germany and the United States that the illness was found associated with the presence of 

 this organism. It has, however, to be noted that in these eases the organism was isolated from impure 

 water which had been drunk by the persons infected or in which they had bathed. 



"Now there is no evidence that the water in No. 6 Well is in any way contaminated by excretal products. 

 The reverse is the case, for the standard indicator of impurity, B. coli communis, has never been found in it. 

 While there are limits to the value to be attached to the chemical and bacteriological analyses of water, still 

 a vast amount of most reliable evidence goes to show that the absence of B. coli from the water is the best 

 known criterion of safety as regards water-borne diseases. This is the view I was inclined to adopt in the jjresent 

 instance, but as the matter was one of great interest and importance and as the organism has been ))roved 

 pathogenic to man and was found to be highlj' virulent to certain rodents, I thought it well to lay the case before 

 Dr. A. 0. Houston, Director of Water Examinations to the Metropolitan Water Board, London, and probably the 

 leading water bacteriologist of the present day. He has confirmed this view and states definitely that, although 

 he has encountered chromogenic glucose (and sometimes lactose) fermenting microbes in well-water, he does not 

 condemn the supply, other things being satisfactory and B. coli being absent. Acting on this ])rinciple, which 

 appears to me eminently sound, I have passed No. 6 Well, more especially as the B. prolcus fluorcsccns had 

 disappeared from the water towards the end of the trials. 



"Passing now to the consideration of Well No. 5, we find the problem is somewhat different. The water is 

 clearly not derived from pfecisely the same source as in the case of the other wells. This is evident from its 

 uniformly lower temperature, which no consideration of the pipe arrangements, etc., will explain. Moreover, the 

 bac-tcriologicjil content differs to some extent. The colony count was more variable and uot quite so satisfactory. 

 Chemically, also, there are slight, but possibly significant, differences {vide Dr. Beam's report, page 312). Thus, 

 although B. coli has never been fonnd in this water, the facts stated, together with the constant presence 



• It is interesting that the air blown into the water did not in any way seem to affect the colony count. 

 At first it was carefully filtered, but afterwards this precaution was abandoned, for observations made by 

 Mr. Williams showed that the 500 cubic feet of free air passing per minute through the cylinders was probably 

 subjected to a temperature of 220° P. This, though but momentary, would, I think, serve effectually to sterilise it. 



t This bacillus was present as a rule in 5 c.c. and larger quantities but was not infrequently found in 1 c.c. of 

 the water. 



