The presence of chlorin in a sample of water indicates the existence therein of certain soluble chlorids. Among these common salt is the most frequent. The presence of chlorin in drinking water, due to a small content of common salt, is normal and unobjectionable. Experience has shown that the water derived from the springs and wells in places remote from the ocean and from centers of salt deposits contains only a very small quantity of common salt. If a larger quantity of chlorin than would be due to this source is found in the water, the first inquiry to be made is whether or not the source of it is near the ocean or a salt mine. If this is the case, the excess of chlorin is not open to suspicion. If, on the other hand, the source of the water is not contaminated by natural salt deposits, then the presence of the excess of chlorin is indicative of contamination with sewage or waste. The urine secreted from human and other animals is extremely rich in common salt, and hence the justification of the suspicion, where a high content of chlorin suddenly appears, of contamination with sewage. In the interpretation, therefore, of analyses, where a large amount of chlorin is indicated, the point of most importance is whether or not this is a normal condition or one which is produced by the abnormal conditions above described.