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Bacteria in Water Supplies Part 2: How to Disinfect Your Well John M. Jemison, Jr., Extension water quality and soil specialist Introduction Bacteria are single-celled organisms found in soil, on our bodies, on leaf material, in lakes, rivers and streams. While surface waters commonly have bacteria, most groundwater supplies do not. This is because the conditions that favor bacterial growth (food, oxygen, warm temperatures and favorable pH) are not frequently found in groundwater. Yet, many wells still have bacteria. Bacteria may carry diseases such as typhoid, dysentery and cholera. In drinking water, these bacteria can cause serious health problems. For example, in Missouri, four people died and 243 people became ill from drinking water with a strain of Escherichia coli (Geldrelch et al., 1992). The water you use for drinking and cooking must be free of pathogenic bacteria. Whether you will get sick after drinking water from contaminated sources depends on the strength of the bacterial strain, the strength and health of your body, and the number of bacteria in the water. Unlike most chemicals, one low-dose exposure to some bacteria can cause serious ill effects (Adamson et al., 1993). If you have bacterially contaminated water, you need to drink bottled water until you have properly disinfected the well. State and federal governments require all public water supplies to be safe. However, you, as the homeowner, are responsible to ensure that your water supply is safe. Bacterial contamination is the most common water quality problem in Maine. In Bulletin #7114, “Bacteria in Water Supplies, Part 1: Problem Bacteria and How to Test for Them,” we discussed how bacteria get into water supplies and water tests. In this fact sheet, we will discuss how to safely disinfect a well. Disinfection Methods If your water test results tell you that you have bacteria in your well water, you must not drink the water until it has been disinfected. One way to be sure drinking water is free from bacteria is to boil the water for five minutes. However, this does not really solve your problem. You still have a contaminated well. The bacteria in the well water, attached to the well casing, and in your plumbing also need to be killed. Treat your well, then do another water test. If bacterial problems come back after you treat the well, then you need to identify the source of the bacteria and try again. See the The Safe H(2)OME Program Fact Sheet Series for information on keeping your well safe. Whatever you do, you want as safe a process as possible, with as little damage to positive organisms, your plumbing or your health. Most disinfection chemicals are toxic. Be careful when you use them. The chemical you use for disinfection should be registered for use in Maine. As of 2004, there are 115 products registered for use in human drinking water as disinfectants (disinfectants are pesticides). Legally you are not permitted to apply a pesticide unless you have the specific label instructions. Often these label instructions are only available from the manufacturer as a supplemental label. Table 2 contains the supplemental directions for Ultra Clorox®, however each disinfectant is different and you should obtain and use the correct label directions. For more information about pesticides labeled for use for drinking water disinfection in Maine, contact the Maine Board of Pesticides Control at 207-287-7545. Chlorination Chlorination is probably the most common way people disinfect small public and private water supplies in Maine. It is an accepted standard method against which most other methods are compared. Chlorine will also react with organic materials, breaking them down into simpler compounds. This is important to know because some of the chlorine you use to purify your water will get used up oxidizing material. This is called "the chlorine demand" of the water supply. It affects how much chlorine is left to attack bacteria cell walls. So, for chlorination to work, you need
If you have both, you'll be able to kill the bacteria. Chlorination Methods Most private wells and water systems can be disinfected with one chlorine treatment. In most cases, if the well requires a chlorination system, either it is not structurally sound, or bacteria are getting in without filtration. Shock chlorination involves a one-time, high-level chlorination process. It's useful when you finish or repair a well or want to treat a contaminated well. See Table 1 for the steps required for shock chlorination. Sometimes a continuous chlorination system is necessary—for instance, a continual problem with iron bacteria can be solved with a simple chlorination system. Simple chlorination systems keep a low level of chlorine in the water (0.2 to 0.5 milligrams per liter) for 30 minutes. Public water systems are required to maintain a 0.2 to 0.7 milligram-per-liter chlorine residual after a 10-minute contact time. Contact a water treatment professional for more information. Trihalomethanes When chlorinating water supplies, you need to be careful that trihalomethanes (THMs) don't form in the process. These chemicals form when free chlorine reacts with natural organic substances. Methylene chloride, bromodichloromethane and chloroform are examples of THMs. These chemicals are considered carcinogens. Several studies have shown that they may increase your risk of getting pancreatic, bladder or rectal cancers (Ijsselmuiden et al., 1992; Morris et al., 1992). However, remember that
If you shock-chlorinate and purge your well system, the chance of having any THMs is very low. On the other hand, if you take water from a lake or pond and super chlorinate the water, there is more organic material in the water and the potential for THM formation is higher. Other Disinfection Methods Chlorination is the most common disinfection method. However, there are others, such as ultraviolet radiation (UV). This method uses light to kill microorganisms. You need a LJV sensor to find the dose of UV light needed to kill the bacteria. Also, water must be clear for UV to work well. UV is recommended for people who prefer not to drink chlorinated water. Ozonation is another water treatment method. It is more powerful than chlorination and is used by many public water supply companies. The disadvantage is that ozone cannot be purchased; it must be generated. The process is more complicated than chlorination, and there are few benefits for the homeowner. The Maine Bureau of Health’s Environmental Health Unit provides advice to private well owners on well water safety. They are available to help interpret the results of well water tests (toll-free in Maine: 866-292-3474). For more information on water quality, water testing or other issues, contact your county office of the University of Maine Cooperative Extension. References
For more information, contact your UMaine Extension county office. © 2002 Published and distributed in furtherance of Acts of Congress of May 8 and June 30, 1914, by the University of Maine Cooperative Extension, the Land Grant University of the state of Maine and the U.S. Department of Agriculture cooperating. Cooperative Extension and other agencies of the U.S.D.A. provide equal opportunities in programs and employment. Call 800-287-0274 or TDD 800-287-8957 (in Maine), or 207-581-3188, for information on publications and program offerings from University of Maine Cooperative Extension, or visit www.extension.umaine.edu.
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04/30/08
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