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Coliform Bacteria

About Coliform Bacteria

Coliform bacteria are a diverse category of bacteria found in almost every environment. They can be found in soil and surface water and on your skin. Human and animal waste also contains large quantities of some types of coliform bacteria. Although most coliform bacteria are safe for humans, a few can cause minor infections, and some can cause catastrophic waterborne illnesses.

Coliform Bacteria

Coliform bacteria are also called indicator microorganisms because they are found in contaminated water, and hence they are responsible for causing waterborne diseases. They are only detrimental when their quantity increases in the water. But the presence of coliform bacteria in the water does not mean that that water will make you sick. Instead, it means that the water is contaminated with the bacteria, and there is a clear channel between the source of bacteria and the water supply.

Various tests can identify the presence or absence of coliform bacteria in the water sample. Once there is a positive coliform bacteria test report, other tests can also be performed to identify the specific kind of coliform bacteria present in the water. The two most common subgroups of coliform bacteria are fecal coliform Bacteria and Escherichia coli. Fecal coliform bacteria are present in the intestine of warm-blooded animals, that is, humans and other animals. A sewage test or animal waste contamination test is required to identify the presence of these fecal coliforms. E. coli is a kind of fecal coliform bacterium that may be found in both animals and people's intestines.

If the test is positive for E.coli, that means the water is highly contaminated because the presence of e coli in the water means that animal or human waste has entered the supply water. Numerous strains of e coli exist which can enter the water supply. Although most strains are present inside humans and animals' small and large intestines, and they are also safe, some strains can still create a potent toxin, causing serious sickness and death.

Coliform Bacteria's Health Effects

As already stated in this article, the presence of coliform bacteria in the water does not mean that it will result in sickness or any disease. There are some very common signs of bacteria that cause diseases. Some of them are fever, diarrhea, flu-like symptoms, gastrointestinal discomfort, and stomach cramps. The majority of these microorganisms are completely safe for humans.

Coliform Bacteria

Children and elderly family members are most prone to exhibit symptoms. People living in a certain area who have the habit of drinking the water of that area have the chance of developing immunity to the bacteria present in their drinking water. Hence, they will show no signs of sickness. However, people who are not the residents of that area have not developed any immunity, and hence they may feel unwell after drinking that water. Another issue is that the signs and symptoms of diseases caused by coliform bacteria are very similar to many human diseases. Therefore it is very difficult to determine the root cause of the problem without analyzing the water.

Standards for Drinking Water

The majority of coliform bacteria do not cause disease, but the higher their quantity, the more likely disease-causing bacteria are present. The lack of coliform bacteria leads people to believe that the supplied water is bacteriologically safe for human consumption. As a result, the drinking water standard stipulates that no coliform bacteria be present. Drinking water should also be free of fecal coliform and E. coli bacteria.

Coliform Bacteria Testing in Water

Obtaining a sterile sample vial from the laboratory and collecting the sample properly according to their instructions is essential for proper water testing for microorganisms. If the sample is not collected in a sterile container, microorganisms may be introduced during the collection procedure.

Different techniques have been developed to test the water for the coliform bacteria in the laboratory. The most common way is to collect the bacteria and run 100 ml of water through a membrane filter. The same filter is then placed in a Petri dish for the whole night along with the agar to cultivate bacteria. If the water sample has bacteria present, they will show visible colonies that are countable on the filter paper; if there are no bacteria, there will be no colony visible.

The findings of coliform bacteria may simply be expressed as "present" (P) or "absent" (A) (A). The term present simply means that in 100 ml of a water sample, there is at least the presence of one bacterium. Other bacteria-testing methods include searching for color changes in test tubes after incubating a water sample. These methods of analyzing water are very simple, faster, and less costly than other approaches, and therefore these methods of explaining the presence or absence of bacteria have grown popular. However, they give less information on the severity of the bacterial issue, which might be useful in determining causes and treatments.

Other coliform-bacteria testing methods rely on color changes and yield a count of bacteria. They rely mainly on the statistical results to estimate the number of bacteria present in the water sample based on the change of color in numerous test tubes. A very common term, "most probable number," is usually used with such approaches.

These are known as the "most probable number" (MPN) approaches. They rely on a statistical connection to estimate the number of bacteria in your sample based on color changes in numerous test tubes.

Coliform bacteria findings are sometimes referred to as "TNTC" (too many to count) or "confluent." TNTC refers to a bacterium concentration that was too high to count (generally higher than 200 colonies per 100 mL). Confluent denotes that a large number of no coliform bacteria developed on the plate, making coliform bacterium identification difficult. In either situation, a second sample should be sent to the laboratory for a more precise analysis.

How Common Are Coliform Bacteria?

Coliform bacteria are a major source of water pollution around the world. No water is free from coliform bacteria, and because of this, coliform bacteria are called Omnipresent and are present everywhere. According to the data of 2006, in one of the states of the United States, 450 private wells were examined for coliform bacteria, and out of these, e coli was present in 15% of the wells and 35% of the wells contained coliform bacteria. Soil and rocks naturally filter the water from coliform bacteria.

Coliform Bacteria

When surface water infiltrates into the ground, coliform bacteria are far more frequent in springs and shallow wells than in deeper wells. Deeper wells (more than 100 feet) can still be polluted by coliform bacteria if they are incorrectly designed, enabling surface water to flow straight into deep groundwater or if surrounding land uses are contaminating deep groundwater.

Coliform Bacteria

Removing Bacteria from Drinking Water

Problems with coliform bacteria-positive wells or springs can occasionally be rectified with relatively easy activities. If the water supply tests positive for the presence of coliform bacteria, take the following procedures to address the issue.

  • Test results must be confirmed: Make sure the coliform bacteria test you obtained is correct before you make any costly decisions concerning your water source. Use a competent water-testing facility and carefully follow the sample collecting method with a sterile sample bottle. You might wish to submit a second sample merely to validate the first. In addition, if you simply got a presence/absence test, you might wish to ask the lab technicians to count the bacteria in the water sample. If the water sample is found positive for the presence of coliform bacteria, an additional E. coli bacteria test can assist in establishing the severity of the bacteria problem.
  • System Maintenance: Simple upkeep of the water supply can sometimes eliminate the cause of bacterial contamination. To prevent surface water from entering the well, you may wish to extend a buried well casing above ground and slope the ground away from the casing. Also, ensure that the casing's top has a tight, hygienic well cap that keeps insects and surface water out. Consider converting to a sanitary well cap if you have a loose-fitting basic well cap. If you have a spring, ensure sure the spring box is properly sealed to keep insects and animals out. If E. coli bacteria are found, inspect your septic system and remove or redirect visible sources of animal feces from surrounding the well or spring.
  • Shock Chlorination: In rare situations, coliform bacteria can enter a well or spring as a result of a one-time or transitory contamination events, such as a severe downpour or the construction of a new submersible pumping system. Disinfection of a well or spring can be carried out by adding a high quantity of chlorine into the water for a very brief period of time. This is called shock chlorination, and this method has been proved very helpful. After adding chlorine, test the water sample again for the coliform bacteria within 10 to 14 days and then again some months later. If the subsequent coliform bacteria tests are negative, it is possible that the contamination was a one-time incident that was properly addressed. If the germs have reappeared, you should choose a continual disinfection treatment system like those outlined below.
    According to Penn State research, around 15% of coliform bacteria-infected wells might be cured by shock chlorinating the well and placing a sanitary well top. This was notably true for wells with a low concentration of coliform bacteria (fewer than 10 colonies per 100 mL).
  • Continuous Disinfection: If the shock chlorination method somehow fails to remove coliform bacteria from the water supply, one may consider purchasing a disinfection treatment process that constantly treats all water entering the residence. Several commercially available disinfection treatment systems use the techniques mentioned here.

Continuous Disinfection Methods


To ensure that the water is bacteria-free, the municipal corporation constantly adds chlorine to their water supply. In order to do so, there is a mechanism of feed system injection where they inject chlorine solution or dry powder chlorine into the water body ahead of the storage tank in the treatment system. Other systems may distribute chlorine using suction-type chlorinators or pellet droppers.

The water must be free of any suspended sediment or cloudiness for the system to work efficiently before entering the chlorinator. A sediment filter is commonly fitted before the chlorinator to remove tiny quantities of suspended particles.

The purpose of constant chlorination is to produce enough chlorine to meet the chlorine demand while still leaving around 0.3 to 0.5 milligrams of residual chlorine in the water. This residual chlorine can then be used to destroy microorganisms that enter the water after the chlorinator.

Coliform Bacteria

The contact time is the amount of time it takes for chlorine to destroy microorganisms. The needed contact time will vary based on the water properties, but a reasonable rule of thumb is to allow for 30 minutes of contact time. Standard pressure tanks are frequently insufficient to give enough contact time. Hence a bigger alternate holding tank may be required. Passing the water through a network of coiled pipes can also provide enough contact time. Increasing the chlorine dosage (super chlorination) can reduce contact time. However, this may necessitate the use of a carbon filter to eliminate the undesirable chlorine taste and odor.

Continuous chlorination treatment systems need extensive maintenance. Chlorinators must be examined on a regular basis to guarantee good operation, and chlorine sources must be refilled on a regular basis. Both liquid and solid forms of chlorine are toxic, and irritants must be handled with extreme caution.

Ultraviolet Light

Since it does not add any chemicals to the water, ultraviolet (UV) light is becoming a useful solution for disinfection treatment. UV light systems, however, are not advised for water sources with total coliform bacteria counts above 1,000 colonies per 100 mL or fecal coliform bacteria counts over 100 colonies per 100 mL.

The device comprises a UV light bulb enclosed in a quartz glass sleeve. As water passes over the glass sleeve, it is treated with UV radiation. To allow the light to reach all the bacteria, the unprocessed water entering the unit must be entirely clean and devoid of any total suspended solids or turbidity. A sediment filter is frequently fitted upstream of the UV unit to eliminate any sediment or organic debris that may enter the unit. The quartz glass sleeve should also be kept clean. Cleaning solutions may be used overnight to maintain the glass sleeve clean, or supplementary wipers can be bought with the machine to clean the glass manually. High hardness (calcium and magnesium) water might even coat the sleeve with scale (a yellowish layer of hardness), necessitating frequent cleaning or the inclusion of a water softener. The device also requires power, which may result in a modest but noticeable rise in your monthly energy bill.

UV systems require little maintenance. However, the light bulb will gradually lose strength over time and need to be replaced roughly once a year. Some versions have a UV light intensity sensor for detecting when the bulb is not generating enough UV light. These sensors raise the unit's initial cost but may pay for themselves after extended bulb life. The downside of this technology is that it only kills bacteria within the unit and does not give any residual disinfection for bacteria that might also escape or be reintroduced into the pipes after the UV light unit has been turned off.

Coliform Bacteria

Other Options

Water can be disinfected using a variety of alternative treatment methods. For a number of reasons, they are not advised for continuous disinfection.


Bacteria are successfully killed by boiling water for around one minute. This procedure is widely used to purify water during an emergency or while camping. However, boiling takes time and energy and only produces a little volume of water. It is not a long-term or continuous water supply disinfection solution.


Ozonation has garnered increased attention in recent years as a strategy for resolving water quality issues such as bacterial infestation. Like chlorine, Ozone is another powerful oxidant used to kill bacteria. Still, Ozone is a comparatively much more unstable gas that must be created using electricity on-site. Once Ozone production is successful, it is injected into the water body, where it kills the harmful bacteria. Ozonation units are not often advised for disinfection since they are significantly more expensive than chlorination or UV light systems. They may be effective if several water quality issues are addressed, such as disinfection in conjunction with iron and manganese removal.


Just like chlorine, iodine has also been used in the past to disinfect the water. Still, due to various health issues about the long-term exposure to iodine, even in low quantities, the idea was dropped off. Chlorine came into place right now, iodination is no more considered a strategy to disinfect the water, but in case of emergency, disinfection iodination can be preferred for a very short period of time. Iodine pills are a common alternative for water cleaning among campers and hikers.

Next TopicBacterial Diseases

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