then, relates to the extent of pollution permissible and still not make the waters unsafe after reasonable filtration. Giving proper weight to the effective work that can be expected of modern water filters, it is not necessary to specify a very rigid or exatcing standard for the raw water subjected to filtration. An approximate figure, which will reveal a water not extremely polluted, will be satisfactory. On this basis the speaker and his colleagues before the commission fixed a standard for a yearly average by the presumptive method, reasonably checked by confirmatory tests, of testing coli whereby positive results in 0.1 cubic centimetre samples of water should not occur in more than fifty per cent. of the samples. Averaging this in an arithmetical way, it would mean that there would be not more than about 500 B. coli in each 100 cubic centimetres of water. It is, of course, to be understood that such arithmetical averaging is not exactly possible, and the results will not correspond in taking one 100 cubic centimetre sample and in taking one hundred I cubic centimetre samples, or one thousand o.1 cubic centimetre samples.

It is not to be assumed, on this basis, that it is impossible to filter properly a water in which the coli content is in excess of the amount here specified. A water may indeed show a much higher coli content and yet be filtered and sterilized after filtration, so that the resulting effluent will be highly satisfactory for all domestic consumption. Nevertheless, there is a good deal of question, as a matter of broad sanitary policy, whether water which is later to be used for drinking should regularly be allowed to become polluted at the intake to a water supply plant in excess of the amount specified. This standard, indeed, is reasonably liberal, and only unusual conditions will make necessary any very expensive purification of sewage wastes in order to keep water for filtration within the limits of this standard.

Table IV shows B. coli content in various water supplies. The results shown here are given on the basis of coli content in one cubic centimetre and in nearly all cases the coli bacilli occur only part of the time in the one cubic centimetre test. In the case of the Lawrence, Mass., water taken from the Merrimac River, and of the Albany, N. Y., water taken from the Hudson River, coli are to be found in 100 per cent. of the tests of the water, and, while the data are not shown in this table, the water roughly approximates to that of the standard tests. Experience has shown, too, that

these waters, which are the worst permissible by this standard for filtration purposes, are satisfactorily filtered by the Lawrence and Albany filters, and that the resulting effluent is reasonably satisfactory bacterially for drinking purposes.

In view of the importance of the pending investigations into

the control of the pollution of the boundary waters between the

United States and Canada, it will not be out of place to include here the guiding principles put before the commission by the sanitary engineers whom they consulted, as follows:

"New York, June 27, 1914.

"To the International Joint Commission.

"Gentlemen: The following statements represent the essence of the opinions given by us before your honorable commission at the conference held in New York on May 26 and 27, 1914:

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"1. Speaking generally, water supplies taken from streams and lakes which receive the drainage of agricultural and grazing lands, rural communities, and unsewered towns, are unsafe for use without purification, but are safe for use if purified.

"2. Water supplies taken from streams and lakes into which the sewage of cities and towns is directly discharged are safe for use after purification, provided that the load upon the purifying mechanism is not too great and that a sufficient factor of safety is maintained, and, further, provided that the plant is properly operated.

"3. As, in general, the boundary waters in their natural state are relatively clear and contain but little organic matter, the best index of pollution now available for the purpose of ascertaining whether a waterpurification plant is overloaded is the number of B. coli per 100 cubic centimetres of water expressed as an annual average and determined from a considerable number of confirmatory tests regularly made throughout the year.

"4. While present information does not permit a definite limit of safe loading of a water-purification plant to be established, it is our judgment that this limit is exceeded if the annual average number of B. coli in the water delivered to the plant is higher than about 500 per 100 cubic centimetres, or if in o.1 cubic centimetre samples of the water B. coli is found fifty per cent. of the time. With such a limit the number of B. coli would be less than the figure given during a

part of the year and would be exceeded during some periods.

5. In waterways where some pollution is inevitable and where the ratio of the volume of water to the volume of sewage is so large that no local nuisance can result, it is our judgment that the method of sewage disposal by dilution represents a natural resource, and that the utilization of this resource is justifiable for economic reasons, provided that an unreasonable burden or responsibility is not placed upon any waterpurification plant and that no menace to the public health is occasioned thereby.

"6. While realizing that in certain cases the discharge of crude sewage into the boundary waters may be without danger, it is our judgment that effective sanitary administration requires the adoption of the general policy that no untreated sewage from cities or towns shall be discharged into the boundary waters.

"7. The nature of the sewage treatment required should vary according to the local conditions, each community being permitted to take advantage of its situation with respect to local conditions and its remoteness from other communities, with the intent that the cost of sewage treatment may be kept reasonably low.

“8. In general, the simplest allowable method of sewage treatment, such as would be suitable for small communities remote from other communities, should be the removal of the larger suspended solids by screening through a one-fourth-inch mesh or by sedimentation.

"9. In general, no more elaborate method of sewage treatment should be required than the removal of the suspended solids by fine screening or by sedimentation, or both, followed by chemical disinfection or sterilization of the clarified sewage. Except in the case of some of the smaller streams on the boundary, it is our judgment that such oxidizing processes as intermittent sand filtration, and treatment by sprinkling filters, contact beds, and the like, are unnecessary, inasmuch as ample dilution in the lakes and large streams

will provide sufficient oxygen for the ultimate destruction of the organic matter.

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"10. Disinfection or sterilization of the sewage of a community should be required wherever there is danger of the boundary waters being so polluted that the load on any water-purification plant becomes greater than the limit above mentioned.

"II. It is our opinion that, in general, protection of public water supplies is more economically secured by water purification at the intake than by sewage purification at the sewer outlet, but that under some conditions both water purification and sewage treatment may be necessary.

"12. The bacteriological tests which have been made in large numbers under the direction of the International Joint Commission indicate that in most places the pollution of the boundary waters is such as to be a general menace to the public health should the water be used without purification as sources of public water supply or should they be used for drinking purposes by persons travelling in boats.

13. It is our judgment that the drinking water used on vessels traversing boundary waters should not be taken indiscriminately from the waters traversed, unless subjected to adequate purification, but should be obtained preferably from safe sources of supply at the terminals.

14. While recognizing that the direct discharge of fecal matter from boats into the boundary waters may often be without danger, yet in the interest of effective sanitary administration it is our judgment that the indiscriminate discharge of unsterilized fecal matter from vessels into the boundary waters should not be permitted.

"Yours respectfully,

"GEORGE W. FULLER, EARLE B. PHELPS, GEORGE C. WHIPPLE,

W. S. LEA,

T. J. LAFRENIERE."