Often data which are perfectly reliable concerning a product like water are interpreted in entirely different ways by reason of different points of view. The expert who is employed by the manufacturer will interpret a given set of data in a manner entirely exonerating the manufacturer from any blame either of wilful contamination or criminal negligence. The same data interpreted by an expert representing the consumer may lead to a condemnation of the sample as not suitable for consumption. It is safe, as a rule, to follow the opinions of the expert in the interests of the consumer. To follow the conclusions of the expert for the manufacturer may lead to grave injury. On the other hand, to follow the opinions of the expert for the consumer cannot possibly injure anyone except the producer himself. Very bitter contentions have arisen before the courts regarding this matter, and the courts have interpreted the data differently. Upon the whole the tendency of the judgment of the courts is generally toward the protection of the consumer.

One must take into consideration in this matter various conditions of the environment. The season of the year, the proximity of possible sources of contamination, the magnitude of the flow, the general history of the locality, the dip of the rock strata, the general geological formation, the trend of drainage areas and the character and quality of the soil underlying rocks, are all to be considered.

In general it is safe to follow the rule that all waters intended for drinking purposes which show the presence of colon bacillus in a majority of samples of one cubic centimeter, should be considered as polluted and excluded from consumption. While the application of this rule might exclude some samples which are wholly innocuous, the failure to observe it might admit many others that are dangerously contaminated. The application of science and bacteriology to the study of potable waters and potable mineral waters has been practised only for a few years, and the full benefit which is to come from such examination has not yet been realized. In these circumstances it is not wise to listen to the advice of some few scientific men who speak with some contempt of the efforts which are made to judge the waters by bacterial methods.