CHEMICAL EXAMINATION OF THE WATEK SUPPLY. 283 
the potability of a given water from the chemical analysis alone, but 
that in order to form a correct opinion on this point, three things at 
least have to be taken into consideration: First, the source of the 
water and the sanitary conditions of the watershed; second, the 
number and character of the microorganisms present in the water ; and 
third, the chemical composition of the water, or rather the nature and 
amount of the impurities contained therein, paying particular atten- 
tion of course to those substances whose presence in quantities over 
and above certain more or less arbitrarily fixed amounts have gen- 
erally been agreed upon by investigators in this field as indicating 
pollution, viz, chlorine, nitrogen in the form of free and albuminoid 
ammonia, nitrites, nitrates, oxygen required, etc., and also to the 
gross physical characteristics of the water, such as color, turbidity, 
odor, sediment, etc.® 
According to Whipple^, a pure and wholesome water — 
must be free from all poisonous substances, as the salts of lead; must be free from bac- 
teria and other organisms liable to cause disease, such as the bacilli of typhoid fever or 
dysentery; it must also be free from bacteria of fecal origin, such as B. Coli. In other 
words, the water must be free from poisonous substances, from infection, and even 
from contamination c. Besides this, it must be practically clear, colorless, odorless, 
and reasonably free from objectionable chemical salts in solution and from microscopic 
organisms in suspension. Moreover, it must be well aerated. Color, turbidity, odor, 
dissolved salts, etc., may be permissible to a small degree without throwing the water 
outside of the definition of pure and wholesome waters. In these minor matters, local 
standards govern up to a certain point, and it is in regard to them that differences in the 
judgment and experience of analysts lead to different classifications. 
According to the same author: 
If the water under consideration has been used for a considerable time, the typhoid 
fever death rate of the community will fairly well represent the sanitary quality of the 
water supply. It will not tell the whole story, but in many cases it will not lead far 
astray. 
A consideration of the results of our own analyses and those of 
other analysts, of the several water supplies of the District of Colum- 
bia, in the light of these several criteria for judging the purity and 
wholesomeness of a water, leads to the following conclusions : 
It will be seen from the summaries of analyses given in Tables 
1 and 2 that the water of Dalecarlia reservoir at the inlet shows more 
See the following authorities: Mason, Water Supply (1898), p. 360; see also Mason, 
“Examination of Water” (1901), Introduction, pp. 1-6; also Clifford Richardson, 
“ Characteristics of Well and Spring Waters in a Thickly Populated Area,” Jour. Anal, 
and Appl. Chem., Vol. V (1891), p. 22, section 5. Palmer, “Chemical Survey of the 
Waters of Illinois” (1903), pp. 37-41. Richards and Woodman, “Air, Water, and 
Food ” (1901), pp. 67-81. Leffman,* “ Examination of Waters,” 5th ed. 1903, p. 10*8. 
& “The value of Pure Water,” by George C. MTiipple, Biological Studies by the 
Pupils of William Thompson Sedgwick, Boston, 1906, p. 54-77. 
c In a footnote this author says by this term (meaning contamination) is meant 
pollution with fecal matter. Contamination must be considered as potential 
infection. 
