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The smallest of the infectious microorganisms is that group of parasitic forms known as viruses. Too small to be seen under a microscope, viruses are capable of causing disease in both plants and animals. Viruses can pass through porcelain filters that are capable of screening out bacteria. Viruses, such as those producing infectious hepatitis, poliomyelitis, meningitis, and gastroenteritis, can be waterborne. Drinking water contaminated with any of these viruses is hazardous.
Virus. A minute (0.004 to 0.1 micron in diameter) infectious agent that is much smaller than bacteria. Viruses are generally considered parasites that are incapable of growth except in the presence of living cells. They can be preserved indefinitely even when frozen or dried.
As you can see from even this brief summary, there is a tremendous variety of living organisms in water. To understand and classify their countless varieties requires an immense amount of knowledge and time. Where these organisms are pathogenic or disease-producing, they may make water unsafe to drink. For obvious reasons, even where there is just a possibility that water contains pathogenic organisms, it must be considered contaminated. While there is a large and varied number of pathogens, no single contaminated water supply is apt to contain more than a few of this countless varieties. On one hand, this is fortunate. But at the same time, it makes detection of pathogens extremely difficult in terms of a routine water analysis.
Note: Not only are speed and accuracy essential in testing sources of drinking water for purity, but frequency is also highly important. Municipal systems run tests on a sliding scale: the more inhabitants there are in the community, the more frequent the tests. A sanitary engineer for a community of 10,000 would be required to run a minimum of 10 tests a month; an engineer for a city of 1,000,000 would run 300 water sample tests a month.
Tests on private water systems are seldom, if ever, made. In the vast majority of cases, one sample is taken. If it shows the water is safe, no further tests may be made on that well. Unfortunately, a serious limitation of coliform bacteria tests is that they indicate the condition of a given sample and no more. Once a test shows lack of contamination, there is no guarantee water cannot become contaminated even within a short time. Proper location and construction of a well are important factors. Equally vital is regular chlorination of the water and frequent contamination tests.
Since both speed and accuracy are essential, laboratory scientists need a sure way to expedite detection of pathogens. They have a dependable answer in a group of readily identified organisms that indicate possible contamination. These indicator organisms are the coliform bacteria. (--> Next)