Water Quality

The U.S.A. government mandates that all suppliers of water must test their water supply for contaminants yearly.Water companies run tests constantly checking for contaminants in the reservoir (main water supply) their water comes from.There are many types of water contaminants.Looking for an indicator organism, an organism that is only present when certain contaminants are present, checks for most water contaminants.(Evans, 2001, p. 8) Water-borne diseases are one type of contaminant that needs to be checked for.Water-borne diseases are those diseases that require large amounts of water.Coliform is an example of a water-borne indicator organism that is what is being looked for in water contamination tests.(Tortora, 2001, p. 759)Water sources are checked for contamination because the transmission of water-borne diseases is high because many people share water from the same source.
1. Obtain a small sample of water from the water supply to be tested for contaminants.
2. Using aseptic technique, inoculate a lactose broth and incubate it at 37 degrees for 24 hours.
3. If the result is anything other than the combination of an acidic change in pH indicated by a yellow color and gas indicated by CO2 getting caught in the inverted Duram tube the test was negative, no further tests are needed.
4. If the result is a change in color of the lactose broth to yellow and the production of gas the test was positive, continue on to the Confirmed test
5. Streak an Eosin Methylene Blue (EMB) plate for isolation using technique and incubate for 24 hours at 37 degrees.
6. A positive result is when the colonies are a metallic green color; continue onto the completed test.
7. A negative result is when the colonies are any other color and no further testing is needed because the contamination was not confirmed.

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