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Total Coliforms in Drinking Water: Risks and Solutions

TypeContaminantMax. Contaminant Level Goal (ppm)Max. Contaminant Level (ppm)
Required Treatment Technique
Potential Health Effects from Long-Term Exposure Above the MCL (unless specified as short-term)Sources of Contaminant in Drinking WaterConsumer Treatment MethodOfficial Sources
MicroorganismsTotal Coliforms (including fecal coliform and E. Coli)
Quick reference guide
Rule Summary
0No more than 5% of samples test positive for coliform in a monthUsed to indicate whether potentially harmful bacteria are presentColiforms are naturally present in the environment; as well as feces; fecal coliforms and E. coli only come from human and animal fecal waste.Chlorination, UV light treatment, ultrafiltration, nanofiltration, reverse osmosis systems, distillation, ozone treatmentCDC, CDC
National Primary Drinking Water Regulations List of Contaminants

Coliform bacteria are a significant concern in drinking water, as their presence can indicate contamination that could lead to serious health issues. These microorganisms are colorless, odorless, and tasteless, making them difficult to detect without proper laboratory testing. Sources of bacterial contamination can vary, but common causes include faulty septic systems, runoff from agriculture or animal operations, and breaches in water distribution systems.

The United States Environmental Protection Agency (EPA) established the Revised Total Coliform Rule (RTCR) to protect public health by monitoring and reducing coliform bacteria levels in public water systems. This regulation aims to provide safe and reliable drinking water for consumers throughout the United States.

When coliforms are found in drinking water, immediate corrective actions are necessary to minimize the risk of illness. Understanding and addressing the causes of contamination can help ensure the delivery of clean and safe tap water, safeguarding the health of communities.

 Types of Coliforms in Drinking Water

Coliform bacteria are a group of microorganisms found in the environment, including soil, water, and vegetation. They serve as an indicator for the possible presence of harmful pathogens in drinking water. When detected in drinking water, it signifies potential contamination from fecal matter, surface water intrusion, or other sources of pollution. Total coliforms in drinking water can be detected through laboratory testing.

E. Coli

Escherichia coli (E. coli) is a type of fecal coliform bacteria commonly found in the intestines of humans and animals. The presence of E. coli in drinking water indicates a high probability of fecal contamination and a greater risk of waterborne illness. Some strains of E. coli can cause severe health issues, such as gastrointestinal infections and even kidney failure. Public water systems are required to test for E. coli regularly, and take corrective action if consecutive tests return positive for it, according to the regulatory limits set by the Environmental Protection Agency (EPA).

Fecal Coliform

Fecal coliform is a subgroup of total coliform bacteria that originates specifically from the feces of warm-blooded animals. The presence of fecal coliform in drinking water is a strong indication of sewage or animal waste contamination. This type of contamination can lead to the introduction of disease-causing organisms, like viruses, parasites, and bacteria, into the water supply. Maintaining low levels of fecal coliform is essential for ensuring safe and reliable drinking water for consumers.

Monitoring and controlling total coliforms, E. coli, and fecal coliform levels in drinking water are critical for protecting public health and preventing waterborne illnesses. Regular testing and adherence to the National Primary Drinking Water Regulations are essential measures taken by water suppliers to maintain water quality and safeguard communities.

How to Test for Total Coliforms in Drinking Water

Testing for total coliforms in drinking water is essential to ensure the safety and quality of the water. Total coliforms are a group of bacteria that are naturally present in the environment, but their presence in drinking water can indicate contamination and possible presence of harmful pathogens.

To test for total coliforms, the first step is to collect a water sample using a sterile 125 or 150 mL plastic bottle, as recommended by the United States Environmental Protection Agency (EPA). If the water sample is chlorinated, sodium thiosulfate should be used as a preservative. Keeping the sample cool, ideally below 10°C (50°F), is essential for source water and groundwater samples, and is also recommended for drinking water samples.

When collecting a water sample, it is important to choose a tap without a screen or remove the screen before collection. Let the cold water run for at least 5 minutes before collecting the sample to minimize the risk of contamination. Hold the bottle near the base of the tap and fill it to the recommended level marked on the bottle itself. Do not overfill the bottle.

Once the sample has been collected, it should be submitted to a certified laboratory for testing. The laboratory will perform various tests to determine the presence of total coliforms, fecal coliforms, E. coli, and other bacteria. The results will indicate whether the water meets the acceptable standards for total coliforms and other bacteria, as established by the EPA.

It is important to test drinking water regularly for total coliforms, especially after floods, heavy rainfall events, or when the water source or plumbing have been altered. Regular testing can provide early detection of potential contamination, allowing for necessary treatment and preventive measures.

How to Remove Total Coliforms from Drinking Water

Coliforms are bacteria that can be present in drinking water, which can pose health risks. To ensure the safety and quality of your water supply, it’s essential to understand the various methods available for removing these contaminants. In this section, we will discuss several techniques for eliminating coliforms, including chlorination, UV light treatment, ultrafiltration, nanofiltration, reverse osmosis systems, distillation, and ozone treatment.


Chlorination is a widely used method to disinfect drinking water. It involves adding a small amount of chlorine-based chemicals to the water source, which kills bacteria, including  coliforms. This process is effective, affordable, and relatively simple to implement. However, it may result in a residual chlorine taste or odor in the treated water.

UV Light Treatment

Ultraviolet (UV) light treatment is another effective way to eliminate coliforms from drinking water. This method uses high-energy UV light to kill bacteria by damaging their DNA. UV light treatment is a chemical-free method and does not leave any residual taste or odor in the water. However, it might not remove other contaminants like heavy metals or chemicals.


Ultrafiltration is a filtration process that uses a semipermeable membrane to remove suspended particles, including coliform bacteria, from the water. It is capable of removing particles as small as 0.01 microns, making it effective in eliminating most bacteria. However, this method may not be effective against viruses or dissolved contaminants.


Nanofiltration is a slightly more advanced filtration technique compared to ultrafiltration. This process uses a tighter membrane that can remove smaller particles, including coliforms and some viruses. It’s also effective in removing specific dissolved contaminants from water. However, nanofiltration might not be effective against all types of dissolved substances.

Reverse Osmosis Systems

Reverse osmosis (RO) systems are a popular choice for removing coliforms and various other contaminants from drinking water. RO systems use a semipermeable membrane to filter out impurities and unwanted substances, including bacteria. This filtration technique can remove 99% of all contaminants, but it may be more expensive and produce a large amount of waste water compared to other methods.


Distillation is a process that uses heat to separate contaminants, including coliforms, from drinking water. Water is boiled, and the steam produced is captured and condensed back into liquid form. This method leaves behind impurities and contaminants, resulting in purified water. However, distillation is energy-intensive and may not remove certain volatile contaminants that have a similar boiling point to water.

Ozone Treatment

Ozone treatment is another chemical-free option for removing total coliforms from drinking water. It involves injecting ozone gas into the water, which oxidizes and kills bacteria, viruses, and other pathogens. Ozone treatment is highly effective in eliminating coliforms but will require a professional installation, and the process may produce some byproducts.

In conclusion, there are various methods available to eliminate coliforms from your drinking water. It is essential to weigh the pros and cons of each technique, considering factors such as cost, maintenance, and effectiveness in order to choose the best option for your specific needs.

How Does Total Coliforms Get into Drinking Water

Coliform bacteria are commonly found in the environment, such as in soil, vegetation, and surface water. They can enter drinking water supplies through various ways, which can lead to contamination and potential health risks if not properly addressed.

One possible way for coliforms to get into drinking water is through the infiltration of surface water into the water supply. Surface water from rivers, lakes, or ponds can be contaminated with coliforms from animal wastes, sewage, and other sources. If surface water enters the water supply due to heavy rains, flooding, or compromised infrastructure, it can introduce coliform bacteria into the drinking water system.

Another route for coliform bacteria to enter drinking water is through the failure of the water treatment process. Coliforms can be introduced into the water system if disinfection processes are not effective enough or if water treatment plants malfunction. Furthermore, if the distribution system has leaks, cracks, or faulty connections, coliforms can infiltrate the treated water as it travels to consumers.

Sometimes, coliforms can enter drinking water supplies through cross-connections with non-drinking water sources. For instance, if household plumbing systems are inadequately designed or poorly maintained, contamination can occur when wastewater from sinks, toilets, or other sources mixes with drinking water.

Finally, contamination can also occur in wells, which are commonly used sources of drinking water. Factors such as poorly constructed, damaged, or deteriorated wells and contaminated surface water entering the wells can introduce coliforms into the groundwater supply.

In summary, coliforms can enter drinking water through various pathways, including surface water infiltration, water treatment failures, cross-connections, and contaminated wells. It is essential to monitor and maintain water systems to prevent coliform contamination and protect public health.

Effects of Coliforms on the Human Body

Coliforms are a group of naturally occurring bacteria found in soil, surface water, and even on human skin. While their presence is not always an indication of harmful contaminants, a significant number of total coliforms in drinking water requires attention as they may indicate the presence of more dangerous bacteria, such as Escherichia coli (E. coli).

When drinking water is contaminated with coliforms, it poses a risk to human health. This is because these bacteria can indicate recent fecal contamination, which may also include disease-causing pathogens like harmful bacteria, viruses, and parasites.

It’s important to differentiate between total coliforms and E. coli. While the presence of coliforms in drinking water doesn’t always pose a health risk, the presence of E. coli is a warning sign. E. coli bacteria, when ingested, can result in severe gastrointestinal illnesses, as well as fever, chills, vomiting, and diarrhea.

In order to ensure the safety and reliability of drinking water, public water systems are mandated to consistently test and treat water for coliform contamination. In cases where a contamination event occurs, swift actions must be taken to protect consumers from potential illness.

Preventing and controlling the presence of coliforms in drinking water is crucial for safeguarding public health. Proper water treatment methods, regular testing, and maintaining water distribution systems are keys to ensuring the quality of water being consumed by the public.


Coliforms can be present in drinking water and serve as indicators of water quality. These bacteria are commonly found in soil, vegetation, and surface water sources. While most coliform bacteria are not harmful to humans, their presence in drinking water may indicate issues with water supply systems and the potential presence of harmful pathogens.

To protect public health, it is essential for water providers to conduct regular testing and monitoring for total coliforms. If a water supply tests positive for coliforms, it may necessitate further investigation and possible corrective actions to address potential contamination sources.

In summary, total coliforms in drinking water serve as important indicators for water quality and the potential risk of harmful pathogens. Regular monitoring and testing are essential to ensure a safe water supply for consumers. Maintaining the integrity of water distribution systems and addressing possible contamination issues can help safeguard public health and provide reliable drinking water sources.

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