The Environmental Protection Agency monitors public water systems for contaminants and ensures that the treatment processes are effectively protecting human health. Aside from health-based standards, water must also meet aesthetic standards, such as color and odor. The EPA prescribes specific reporting requirements, analytical methods and water sampling procedures that public water authorities must follow.
Taking Samples
Water from different sources each require different sampling techniques; however, they share the need for safety, uniformity and non-contamination of the sample. According to Michigan State University, when taking a sample of water, it should be assumed that the sample is pure, meaning untreated, and anything that is done to contaminate it will alter the results of the test. Normal levels of chemicals in pure water are very low, so it is extremely easy to contaminate a sample. The laboratory that will perform the analysis has very strict sampling procedures and it is very important that they are followed exactly. The water will be put through a battery of tests to determine what impurities are present. The most common procedures involve using a certified sterile pure sample container. The tester should never touch the rim or the inside cap of the bottle. Testing for different contaminants involves different methods. For example, when testing for coliform bacteria, the water must be run for several minutes before taking a sample. When testing for heavy metals, the water must sit in the pipes for several hours. Once the sample has been retrieved, it should be capped securely, labeled clearly and either shipped immediately to the lab or stored in a refrigerator until it is ready to be shipped.
Laboratory Analysis
Normal or neutral water has a pH of 7.0. A pH meter can determine the pH of the sample, which will indicate any excess alkalinity or acidity. Hard water, which is determined by the concentration of calcium carbonate, causes fouling and fixture and pipe scaling. Tests for coliform bacteria are performed by putting the water in a nutrient medium and finding how many colonies grow in it. Metals such as mercury, arsenic, lead and iron are detected with a number of different analytical tools. In some areas, the water is tested with a radioactivity detector to determine if it contains radioactive gas.
Interpreting the Results
The University of Pennsylvania states that in order to define how much of a particular contaminant is in water, chemists will use different measurements that can be translated into standard units. One example is parts per million, which is the equivalent of milligrams per liter. Coliform bacteria is measured by the number of bacteria per 100 milliliters and indicates animal or human waste pollution. Other measurements indicate natural contamination or industrial and agricultural runoff. They include sulfur, sulfate, nitrogen and nitrate. Natural minerals may include calcium, chloride and iron. The hardness of water is rated using one of several hardness scales. Salinity is determined by how dense the water is, either by percent or parts per thousand.
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