8 MASS. EXPERIMENT STATION BULLETIN 383 



It is only fair to call the reader's attention to the fact that this bac- 

 teriological test is not infallible. Water should not be judged wholly on 

 such a test. A common-sense sanitary survey of the supply and its im- 

 mediate surroundings should supplement the laboratory analysis. In most 

 cases this survey will indicate the source of contamination and the kind — 

 whether it is of human or animal origin. Further, there may be occasions 

 when the laboratory test fails to reveal any contamination, but the sanitary 

 survey may show certain potential sources of contamination. Such a 

 condition should arouse questions about the future purity of the supply 

 even though the present laboratory tests failed to reveal any impurities. 

 This survey will reveal also faulty construction in the supply, which is an 

 important item particularly in shallow dug wells. If persons building 

 new homes in rural areas would only remember to locate their water 

 supply first, and then so construct their homes that the disposal of waste 

 materials can not contaminate the supply, little trouble would ever be 

 experienced with impure drinking water. 



The results of a single analysis are not always too dependable. A 

 drought or a rain storm just previous to sampling can influence the results 

 considerably. As Dr. Feemster points out in his letter to the writer: 



No doubt in your bulletin you will emphasize the fact that bac- 

 terial examination of water should not be depended upon solely 

 to give an idea of the safety of a particular supply since a sample 

 taken during a wet period or after a heavy rainfall might show 

 evidences of pollution of a well which under more favorable cir- 

 cumstances might appear by bacteriological examination to be 

 perfectly safe. 



Careless sampling methods, and careless handling of the sample between 

 sampling and testing, can also influence the results considerably. 



Before concluding this section some mention should be made of chemical 

 tests of drinking water. In the laboratory at the Massachusetts State 

 College chemical analyses of drinking water are not made. One reason 

 is the belief that the bacteriological test is a much more dependable and 

 sensitive test than the sanitary chemical test. The bacteriological test 

 can detect minute amounts of contamination which might be missed in the 

 chemical tests. Further, the chemical analysis is of little value when 

 applied to rural private water supplies unless several such tests can be 

 made over a considerable period of time. Individual waters vary con- 

 siderably in their chemical composition, and unless normals have been 

 established by means of frequent tests it is dii^cult to justify an opinion 

 of the quality of the water upon one test. In the case of town and city 

 water supplies the State Board of Health makes frequent routine chemical 

 analyses of the supplies. This has been done for many years, and in this 

 way it has been possible for them to establish normals for the several 

 chemical components of the water. If at any testing period results show 

 that any one or several of these chemical components varies from the 

 normal, check tests, as well as an immediate sanitary survey, are made 

 to locate the source of the change. Incidentally, the bacteriological 

 analysis is one of the most important check tests. 



In conclusion there is another type of chemical analysis for which 

 frequent requests are made. So far as we know there is no water in the 

 State of Massachusetts that might contain any one, or several, chemical 



