312 



THE WATER-SITPPLY OF TOWNS IN THE TROPICS 



Doubt as to 

 Well No. :. 



Conclusions 

 justified 



of H. imiliiu Jluvrciaiis, led oiic to ro),'iiril tins sotiri'i; of sii|)|)l_v with some suspiiMoii. I tbiiik it would 1h; 

 advisalile not to iwins No. 5 until wc liavo kariiod niort; about it. 'I'hu water would appear to ('onie from nearer 

 the surface. It docs not secui to have any immediate eoiiueetion with the river, aud as the yield is small, would 

 appear to be derived from some bed of limited e.xtcnt which perha])9 trends towards the surface. This is not an 

 easy ciuestion to settle, and of eijual difficulty is the determination of the source of /I. prolciui Amiresrcn.1 l>oth in 

 Well No. 5 and Well No. 6. It ajipcars that adjacent to the water works there is a bed of decomposini; vegetable 

 material close to the southern river bank aud aljout a metre under the river bed. This was encountered when the 

 pipe trenches for the condeusatiou water from the Blue Nile were dut;, but no information was furnislied me 

 on this point and I ouly learned it recently from one of the otlicials. Considering, however, that the cuttinij-otT 

 by cement is s:itisfactory, aud that the deep clay beds appear to be (|uite impermeable, it would not seem that any 

 contamination could be derived from this source, and in any case such contamination mitrht not be of a dangerous 

 nature. The suggestiou has been nuide that the cement used in the cutting-ofT proces.s might have becrome 

 contaminated from the feet of the native workpeople, and that the water-bearing beds had thus been rendered 

 temporarily impure. If this were so, however, one would have e.tpected a much higher colony count and a much 

 greater variety of microljes while some type of Jl. coli would almost certainly have been present, unless, indeed, 

 other organisms, apart from B. proleus ttiu>rescfns, had died out in the pure, deep water. This is not very 

 likely, as certain varieties of B. ei)li are known to be fairly resistant. The organism does not apjx;ar to have 

 come from the air-pipe line. 



" It would serve no purpose to discuss this matter at greater length, but there is one point on which special 

 stress must be laid. T/t^ irsults ohtitined cnn onhi be coiisideral ttpplunbtc to the veils under ej'isliiiJj eonftitiuns. 

 True, the tests have been fairly exhaustive and severe, and, personally, I think it likely that the water in 

 Wells Nos. 1, 6 and 7 will continue to be a safe source of supply, but one cannot be absolutely certain, for it is 

 possible, though not probable, that changes in the river maj' induce changes in the deep water. Hence the 

 necessity for routine bacteriological tests, which, indeed, are nowadays carried out in connection with all well- 

 conducted town supplies. These will be combined with occasional chemical examinations, and this leads one to 

 draw attention to the attached report from Dr. Beam.* On this occasion, chemical tests are of subsidiary 

 importance, but they po,s.sess considerable interest, and, so far as they go, they confirm the bacterioscopic analyses. 



"There is nothing in them to lead to a condemnation of any of the well-waters. The quantities of iron 

 and manganese present are too low to be likely to cause any serious trouble with crenothrix growth, provided the 

 large storage tank, now in course of construction, is in use. At the same time they are undesirable ingredients, 

 though it will be noted that with the exception of Well No. a, they tended to diminish as ))umping proceeded. 

 It will be also noted that the plumbo-solvcnt power of the water was tested, although very little lead piping will 

 l)C used in Khartoum. 



The following conclusions, therefore, appear justifiable : — 



'•1. From a chemical standpoint the four wells tested, Nos. 1, o, G and 7 have yielded a satisfactory water. 



"2. Bactcriologically, Wells Nos. 1, G and 7 have yielded a satisfactory supply. 



".3. Bacteriologically, Well No. 5 has not proved so satisfairtory as the others, and is not passed at present. 

 As a matter of fact, I understand that as there is a low yield from this well the Director of Works has no 

 p.irticular objection to its being closed, and this may possibly be done. 



" 4. The examinations made refer only to the water under existing conditions, though it is believed that the 

 tests have been sufficiently prolonged and severe to make it probable that the supply will remain satisfactory as 

 the source itself seems to be above suspicion. 



" 5. It will be necessary to conduct routine bacteriological examinations and occasional chemical tests while 

 the conditions of storage will require careful consideration. 



" 6. The question of quantity is one for engineers to settle, hut, from the data furnished, there would aj)jK'ar 

 to be an ample supply, at least, for the present." 



I may say these conclusions have so far been amply justified. For a year and more 

 routine tests have been made, the Nile has risen, fallen and risen again, the well-water 

 has been in general use, the quality has remained good, and apart from a little trouble in 

 the pipes owing to crenothrix, the supply has been quite satisfactory. A large covered 

 reservoir has now been constructed and this will tend to improve matters so far as iron 

 is concerned (Fig. 100). 



A paper of this nature should, perhaps, deal with questions of distribution, storage, 

 and methods of water sterilisation in the Tropics, but, owing to lack of local experietice 

 in these directions, such additions would be more or less of the nature of a compilation, 

 and, as they are dealt with in our Second Review, may be omitted, save for some reference 

 to distribution methods in the Appendix. Therefore, I would only again lay stress on 

 the demonstration which has been afforded us of the great value of /}. coli, even Houston's 

 old, merely partially qualified, elastic B. cnii, as a standard of pollution under certain 

 conditions in the Tropics. It would have been most interesting to apply Clemcslia's tests 

 to the B. coli which was found in the deep well-water, but his paper had not Ijceii published, 

 and in any case, time would not have admitted of such a research. I wonder, however. 



* For details of the chemical atuklysos, and full comments upon them, sec Dr. Beam's report, Volume B., p. 2G 



