122 



A. Pedler — On tlie past and present 



[No. 2, 



Taking the numbers representing the general average for the year and 

 comparing them with the standards which I have suggested from Dr. 

 Frankland's works, we find that the Calcutta water falls just outside the 

 class of waters of " great organic purity," but that it is well within the 

 class of waters of " fair organic purity." 



Comparing again the numbers with those given in the previous 

 table we find that the Calcutta Hydrant water though not so pure as the 

 London waters derived from the deep wells in the Chalk, is certainly 

 purer than the waters derived from the Thames, and perhaps also from the 

 Lea. It is also decidedly more free from impurity than the water supplies 

 of Edinburgh, Liverpool and Dublin, but taking all the constituents into 

 consideration, it is not so pure as the Glasgow or Manchester supplies, or as 

 the Rhine water above Schaffhausen. Comparing the Hydrant water with 

 the average composition of unpolluted upland surface water as given by Dr. 

 Frankland, we find that it is scarcely so pure as unpolluted water should be, 

 and we are therefore compelled to admit that the Hooghly water has been 

 slightly contaminated before it reaches Pultah. The amount of contami- 

 nation is, however, not very great and as pointed out before, the Calcutta water 

 falls well within the class of waters of medium purity. That the Calcutta 

 water must be contaminated to a certain extent will be I think obvious 

 to any one who is acquainted with the customs of the inhabitants of India, 

 and more particularly of the inhabitants of villages and towns on the 

 banks of the rivers. This contamination is a drawback to the complete 

 safety of our water supply, for as pointed out previously. Dr. Frankland 

 is of opinion, that a water once contaminated is always dangerous, and 

 that the self -purification of a river which is so strongly insisted upon by 

 certain persons is exceedingly slight. It does not however at present appear 

 to be possible to cut off these sources of contamination, and the Hydrant 

 water though good is not a perfect supply. Every effort however should 

 be made to keep this previous contamination down to the lowest possible 

 point, and it is to be hoped when systems of drainage are being introduced 

 into the up-country towns, that the sewage from them will not be allowed 

 to find its way into our river. Speaking generally the sewage from any 

 one town should not be allowed to find its way into a river which is used as 

 a source of water supply for other towns lower down. 



It is not my intention to criticise these average numbers in detail, 

 but it will suffice to say that from the absence of ammonia and from the 

 smallness of the amounts of organic carbon and nitrogen, and of nitrates 

 and nitrites, and also of chlorine, it is clearly evident that the contamination 

 of the Calcutta water is really much smaller than might have been ex- 

 pected under the circumstances, and we may rest assured that our water 

 supply is of fairly good quality, better in fact than that received by the 

 majority of large towns in Europe. 



