130 A. Petller — On tlie past and present Water supplies of Calcutta. [No. 2, 



were sodium chloride, were found ; again on May 1866, two hours before 

 the commencement of tide, there were 21*50 parts of salt present ; on 

 May 2nd 1866, there were 15'50 parts of salt at ebb-tide, and on June 1st 

 1866 at nearly low water, 16'50 parts of sodium chloride were found; 

 these numbers being the quantities present in 100,000 parts of water. 



With regard to organic matter also Mr. Waldie's results, though 

 showing much less organic matter than Dr. Macnamara's analyses, to a 

 great extent confirm his statements, and prove that as a rule, there is a 

 larger amount of organic matter in the water collected at ebb-tide off 

 Burranagur, than in the water collected at higher points of the river. The 

 numbers above quoted show unmistakeably that at two miles above Oossi- 

 'pore during the hot season, there is a decided admixture of tidal water 

 and probably of sewage contamination with the pure river water, and that 

 this is the case even with samples collected at low water. 



The opinion of Dr. Macnamara as to the suitability of Cossipore 

 water for drinking purposes, has already been given. I will now quote 

 Mr. Waldie's remark in his general summary of results — " Can the supply 

 be safely taken from the river at Cossipore ? We can scarcely answer in 

 the affirmative." 



In conclusion, then, I may say that, so far as can be ascertained from 

 the old analyses by Dr. Macnamara and Mr. Waldie, and from my own 

 results, it is my opinion — 



That dui'ing the rainy season, and whilst the river is in fuU stream, 

 the water collected two miles above Cossipore, or perhaps even at Cossipore, 

 could probably bo used as a fairly safe water-supply. 



That during the hot weather months, if the water is collected two 

 miles above Cossipore, even at five hours' ebb, there will frequently, if 

 not always, be contamination with tidal water to an extent, which unfits 

 it for a safe water-supply, and tlie water will be contaminated to a still 

 greater degree if collected at Cossipore. 



That this tidal contamination would involve also organic contamination 

 to a considerable extent, and that, as pointed out in a previous part of 

 this paper, such organic or sewage contamination cannot become oxidized 

 or destroyed during the flow of the water, nor can the water be purified 

 by the ordinary processes of settling, filtration through sand etc. so as to 

 render it a safe supply for domestic purposes. Such water therefore would 

 be eminently unsafe for potable purposes and should be at once condemned. 



That unless contrary evidence is furnished, the proposed new sources 

 of supply are too near to the mouth of the river and to Calcutta, and 

 consequently that it is strongly desirable that the extension of the water 

 supply should be carried out on the same principle as formerly, and that 

 the water should always be collected at Pultah, and not at the other points 

 which have been suggested. 



