How to Test Water in a Lab

Water is tested for a number of things in a lab, however in most cases people are testing for the purity of their water. Though pure (distilled) water is drinkable, in most cases people are testing tap water or well water and this is never totally pure. Tests are for values within acceptable limits; for levels of hardness, acidity and for contaminants, which can be chemical, particulate or bacterial. The tests described are screening tests. If significantly negative results are detected the sample should be sent to a state health facility for further testing..

Things You'll Need

• 1 Liter container
• Two 500 milliliter beakers
• One dozen test tubes
• Test strips for: Nitrate/nitrite; pH; hardness; lead; mercury; Iron; Chlorine; Copper and arsenic.
• E-coli testing kit

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Instructions

Preparing to test.

• 1

  Collect water from a cleaned tap into sterilized containers.

  Obtain a representative water sample from your source by running water from the well or tap for at least two minutes. Immediately prior to taking the sample, clean the tap or spigot and always collect into a sterile container. If obtaining water from a wetland or other outdoor body of water, collect a sample into a clean container, and then pour into a sterile container, avoiding contamination as much as possible. Observe obvious characteristics, including color, smell and level of turbidity (cloudiness).

• 2

  Bacteria, parasites and chemical contaminants in water can be observed with a microscope.

  Place a drop of water on a glass slide and cover with a cover slip. Place the wet mount under a microscope at 10X magnification and observe for bacteria and parasites, mineral and other microscopic particles. Note the level of debris and other contaminants found.

• 3

  Using water from the sterile container test for specific chemical and other contaminants using test strips. Test strips are available for many chemical contaminants, such as metals, soluble gases and bacteria. The basic method is the same for each. Swish the strip through the water and rest across the mouth of the container until the color change develops. Compare with the given chart and note the level obtained. The same method is used to test for pH, hardness and pesticides, and many types of elements and chemicals, such as lead and mercury.

• 4

  Color changes can be measured with a colorimeter or by comparison with a chart.

  Using colorimetric comparison test kits, test for chemical and bacterial contaminants. The standard method for each of these tests is to pour a sample of water into a test tube and add a specified number of drops of a color change reagent. The color change indicates the presence of the specified chemical or bacteria, the level or intensity of the color indicates the amount, and is detected using a colorimeter or by visual comparison with a chart.

• 5

  Using a similar method, use a test kit for detecting bacteria called fecal coli-forms. (For example: LaMonte or COLI-MOR) If their presence is detected it may indicate the presence of other bacteria, which should be further tested by standard microbiology lab procedures.