The effect of storage on the coliform and Bacterium coli counts of water samples

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Abstract
This investigation has been concerned with the changes that occur in the coliform and faecal coli content of water samples on storage at room and refrigerator temperatures for 6 hr. as compared with those occurring after 24 hr. storage.The examination was conducted by a 70-tube method using twofold diminishing volumes.The percentages of samples showing a significant change corresponding to at least a doubling or halving of the coliform content on storage were: (a) at room temperature after 6 hr. 24.7%, and after 24 hr. 38.3%; (b) at refrigerator temperature after 6 hr. 25.0%, and after 24 hr. 33.9%. The percentages of samples showing a significant change in the faecal coli content on storage were: (a) at room temperature after 6 hr. 18.7%, and after 24 hr. 34.6%; (b) at refrigerator temperature after 6 hr. 10.4%, and after 24 hr. 25.0%. The changes were preponderantly decreases and most of the large changes occurred after 24 hr.The investigation has shown that fewer changes occur after 6 hr. storage than after 24 hr. storage, and that storage for 6 hr. at refrigerator temperature is preferable to storage for 6 hr. at room temperature. Even so, some samples show significant changes after 6 hr. storage at refrigerator temperature; the coliform content is significantly altered in 25% of samples and the faecal coli content in 10% of samples.Samples of water should, therefore, be examined as soon as possible after collection, certainly within 6 hr., and during the period of transport to the laboratory they should be kept cold, if possible by ice.

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