Treating Coliform Bacteria in Drinking Water F-132 Bryan R. Swistock, Extension Associate William E. Sharpe, Professor of Forest Hydrology Paul D. Robillard, Associate Professor of Agricultural Engineering What are coliform bacteria? Testing water for coliform bacteria Coliform bacteria occur throughout the environment. The most common water test for bacteria is for total They are common in waste from humans and ani- coliform bacteria. This test is readily available to the mals. However, some coliform bacteria also occur public and is inexpensive (generally $10 to $30). naturally in soil and in surface water. Many species Water tests for total coliform bacteria can be arranged of these bacteria are harmless to humans while others through a local office of the Pennsylvania Department may cause serious waterborne diseases. of Environmental Protection or by a state-certified Coliform bacteria are often referred to as “indi- commercial water-testing laboratory. A list of cator organisms” because they indicate the potential certified commercial labs can be found in Agricultural for disease-causing bacteria to be present in water. and Biological Engineering fact sheet F-105 Where to The presence of coliform bacteria in water does not Have your Water Tested available from your local guarantee that drinking the water will cause an Cooperative Extension office or on-line at http:// illness. Rather, their presence indicates that a www.wqext.psu.edu. Penn State Cooperative Exten- contamination pathway exists between a source of sion recommends that all private water supplies bacteria (surface water, septic system, animal waste, (wells, springs, etc. serving an individual house) be etc.) and the water supply. Disease-causing bacteria tested for total coliform bacteria every year. If your may use this pathway to enter the water supply. initial water test indicates that total coliform bacteria Specific types of coliform bacteria may be tested are present, additional tests for fecal coliform and E. in water, especially after a total coliform bacteria test coli bacteria may be warranted. is positive. These subgroups of coliform bacteria Proper water testing for bacteria will require that include fecal coliform, and Escherichia coli or E. you obtain a sterilized sample bottle from the coli. Fecal coliform bacteria are specific to the laboratory and collect the sample strictly according intestinal tracts of warm-blooded animals and to their instructions. Failure to collect the sample in humans and are thus a more specific test for sewage a sterile container may cause bacteria to be intro- or animal waste contamination. E. coli is a type of duced during the sampling process. fecal coliform bacteria commonly found in the Once you have your water tested, you will intestines of animals and humans. A positive E. coli receive a water test report from the laboratory. result is a strong indication that human sewage or Results from total coliform bacteria tests are nor- animal waste has contaminated the water supply. mally expressed in the number of bacteria that are There are hundreds of strains of E. coli. Although present in every 100 milliliters (mL) (about half a most strains are harmless and live in the intestines of cup) of water. Some laboratories may simply healthy humans and animals, a few strains can express coliform bacteria results as “Present” (P), or produce a powerful toxin and can cause severe “Absent” (A). In this case, “Present” only indicates illness and death. More common signs of infection that at least one bacterium was present in 100 mL of are gastrointestinal upset and general flu-like symp- water. Occasionally, bacteria results will be ex- toms such as fever, abdominal cramps and diarrhea. pressed as “MPN” which stands for Most Probable 1 Number. This simply means that a statistical rela- testing laboratory and that you carefully followed the tionship was used to estimate the number of bacteria sample collection procedure using a sterile sample in your sample. Finally bacteria results may also be bottle. Even then you might want to collect a second reported as “TNTC” or “Too Numerous To sample just to confirm the initial result. Count”meaning the bacteria concentration was so high that it could not be counted. 2. System Maintenance: Sometimes some simple maintenance of the water supply may eliminate the Drinking water standards source of bacterial contamination. For example, you for coliform bacteria might want to extend a buried well casing above the ground and slope the ground away from the casing to Most bacteria in the coliform group do not cause prevent surface water from entering the well. Also, disease, but the greater their number the greater the make sure the top of the casing has a tight, sanitary likelihood that disease-causing bacteria may be seal that prevents insects and surface water from present. Since coliform bacteria usually persist in entering. If you have a spring, make sure the spring water longer than most disease-causing organisms, box is sealed to prevent insects and animals from the absence of coliform bacteria leads to the assump- entering. Consult Extension Circular #345 – Safe- tion that the water supply is microbiologically safe to guarding Wells and Springs from Bacterial Contami- drink. Consuming water with coliform bacteria nation (available for free from your local Cooperative present may cause fever, flu-like symptoms or other Extension office) for more ideas on maintenance of gastro-intestinal illnesses. Therefore, the drinking your water supply to prevent bacterial contamination. water standard requires that no coliform bacteria be present in drinking water. Fecal coliform and E. coli 3. Shock Chlorination: In some cases, coliform bacteria should also be absent from drinking water. bacteria can be introduced to a well or spring from a one-time or temporary contamination event like an How common are coliform especially heavy rainstorm. It is also possible for bacteria in Pennsylvania? bacteria to be introduced while installing a new submersible pump or while doing other system mainte- Coliform bacteria are one of the most common water nance. Shock chlorination can be used to disinfect a contamination problems in private water systems in well or spring by introducing a high concentration of Pennsylvania and throughout the United States. Past chlorine to the water for a short time. The exact surveys conducted by Penn State University, the U.S. procedure is outlined in Agricultural and Biological Geological Survey and other agencies have found Engineering Fact Sheet F 140 - Shock Chlorination of coliform bacteria to be present in about 40% of all Wells and Springs. Once you have shock chlorinated private water systems. the water supply you should re-test the water for Bacterial contamination is more common in coliform bacteria within two weeks. If the follow-up shallow water supplies, like hand-dug wells or coliform bacteria test is negative, it is likely that a one- springs, than in deep wells. That’s because bacteria time contamination event occurred that has been are naturally filtered out by soil and rock as surface successfully treated. If the bacteria have returned, water infiltrates into the ground. Still, over one-fourth you will need to consider a continuous disinfection of deep wells greater than 80 feet deep have coliform treatment system like those described below. bacteria, presumably from improper well construction that allows surface water to flow along the well casing 4. Continuous Disinfection: If shock chlorination directly into the deep groundwater aquifer. is unsuccessful at eliminating coliform bacteria from your water supply, you’ll need to consider buying a Steps to removing bacteria disinfection treatment system that continuously treats from your water supply all of the water entering the home. Many types of disinfection treatment systems are commercially 1. Confirm test results: Before making any costly available utilizing the processes described on the next decisions about your water supply, make sure that the page. coliform bacteria result you have received is accu- rate. Make sure that you used a certified water- 2 Treatment methods for Continuous chlorination treatment systems require continuous disinfection significant maintenance. Chlorinators must be routinely checked to ensure proper operation and Continuous Chlorination chlorine supplies must be periodically replenished, Municipal water treatment plants throughout the usually on a weekly basis. Both liquid and solid United States continuously add chlorine to ensure forms of chlorine are poisonous and irritants that must that their water is free of bacteria. Chlorination be handled according to specific safety measures. treatment systems are basically comprised of a feed system that injects a chlorine solution (sodium Ultraviolet Light hypochlorite) or dry powder (calcium hypochlorite) Ultraviolet (UV) light has become a popular option into the water ahead of a storage tank. Most chlori- for disinfection treatment because it does not add any nators use positive displacement feed pumps to meter chemical to the water. The unit consists of a UV light the chlorine into the water. Other units may utilize bulb encased by a quartz glass sleeve. Water is suction-type chlorinators or pellet droppers to deliver irradiated with UV light as it flows in a thin film over the chlorine. the glass sleeve. The untreated water entering the The raw water entering the chlorinator should be unit must be completely clear and free from any perfectly clear or free of any suspended sediment or suspended sediment or turbidity to allow all of the cloudiness in order for the chlorine to effectively kill bacteria to be irradiated by the light. A sediment the bacteria. A sediment filter is routinely installed filter is often installed ahead of the UV unit to ahead of the chlorinator to remove small amounts of remove any sediment or organic matter before it suspended material. enters the unit. The quartz glass sleeve must also be The chlorine that is injected into the water is kept free of any film.