They consider reasonably safe water, when it is derived from deep wells, (say 100 feet,) or from deep-seated springs, although it contains previous animal sewage, but does not exceed 10,000 parts in 100,000 parts of water. Suspicious or doubtful water is, first, river or flowing water which exhibits any proportion, however small, of previous sewage; and, second, well or spring water containing 10,000 to 20,000 parts. Dangerous water is, first, river or flowing water which exhibits more than 20,000 parts of previous animal contamination; second, river or flow water containing less than 20,000 parts of previous contamination, coming from sewage discharged into it directly, or mingling with it as surface drainage; third, well or deep-seated springs containing more than 20,000 parts, because previous contamination is in direct proportion to the amount of such contamination. The value of an analysis, sanitarily considered, is questioned. Mr. Simon, medical officer of Her Majesty’s Privy Council, testified, before the Royal Commission on Water Supply, on this point, as follows: “There are dangerous qualities of water supply with regard to which, so far as I know, chemists are totally unable to measure, even to demonstrate the fatal influences that a water may have. A water may be, for instance, capable of spreading the cholera, but chemists be unable to identify the particular contamination which produces that effect. It is, I think, a matter of absolute demonstration that, in the old epidemics, when the south side of London suffered so dreadfully from cholera, the great cause of the immense mortality there was a badness of the water supply then distributed in those districts of London.” Prof. Frankland says: “That we have no reason to believe that the injurious character of either sewage or of the gases from a drain depends fundamentally upon the quality of that sewage or of that gas. In all probability it far more depends upon the quality of the sewage, namely, what it consists of. Now, what is the nature of the poisonous matter in the atmosphere or in the sewage? We do not know that, at all; therefore you can not possibly say when that poisonous matter is got rid of from the water or from the air. Chemical analysis can not do it, for its limit is by the power of weighing and measuring. It is not sufficiently advanced, and is one of the poorest things possible to reach those delicate points.” Vital statistics are sources of reliable information; and from them we can learn more of the propagation or dissemination of certain diseases through the water supply, and the relation of water to health. The cholera epidemics of Great Britain exhibit striking examples. The following are tabulations from the Rivers Pollution Commission Report, 1874: LONDON. YEAR. CHARACTER OF WATER. MORTALITY. RATE PER 10,000.