1. Numerical counts on gelatin media are of very limited value for surface well examinations and are quite useless for open draw-wells. The blood-heat enumeration is of use, but still of but limited value.
2. The influence of rainfall and local conditions generally is marked for this class of waters with regard to their bacterial content.
Whether the well is uncovered, or covered and provided with a pump has a very important influence upon the bacteriological results. For a good many wells which show very bad bacteriological findings the cause of pollution is frequently due to surface pollution rather than to pollution of the ground water through the soil. If these wells are properly protected they will become suitable sources of drinking supply.
3. The results obtained confirm the value of B. coli and streptococci estimations as the best tests by which to judge the freedom from pollution of such waters.
The streptococci results are of great value, only second in importance to the B. coli determinations. In numerical distribution these two organisms closely agree. The presence of streptococci is more reliable as evidence to deduce pollution than their absence is to exclude it.
4. An opinion regarding the freedom of surface wells from pollution is best formed on the basis of combined topographical and bacteriological investigation.
5. Inspection alone is frequently quite insufficient for the purpose of determining if a well is contaminated and if it should be closed.
Of the 50 wells examined no less than 31 had to be classed as doubtful (Series C), topographical examination alone affording insufficient data for the expression of a decided opinion.
In view of the fact that pure water supplies are not easy to obtain in many rural districts, a water supply, which may have been in use for many years, cannot be condemned in the absence of clear evidence that it is unsatisfactory and dangerous.
6. In surface well waters a large proportion of the coli-like organisms isolated are atypical in one or more particulars.
7. Typical B. coli implanted into soil showed some alteration of character, but the changes were not extensive and no evidence was obtained that the widely aberrant organisms met with in different soils and waters ever represent typical B. coli altered by unfavourable environment.
8. Organisms closely allied to B. coli, but differing in one or more characters, possess significance as indicators of faecal contamination.
The more nearly the organism isolated resembles an “excretal” B. coli the greater is its significance as an indicator of pollution. Consequently the fewer the number required to condemn a sample water in which they occur. Stated as a working proposition, the more the characters of the coli-like organisms deviate from that which for convenience may be spoken of as the typical form, the greater the proportionate number of them required to condemn the water.
9. The presence of ‘excretal’ B. coli in 10 c.c. or less of a surface well water points to undesirable pollution and is sufficient to condemn the water.
