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Giardia Lamblia in Drinking Water: Risks and Prevention Methods

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
MicroorganismsGiardia lamblia0Treatment Technique (99.9% removal/inactivation)Gastrointestinal illness (such as diarrhea, vomiting, and cramps)Human and animal fecal wasteBoiling water, UV light treatment, microfiltration, ultrafiltration, nanofiltration, reverse osmosis system, distillation, Ozone treatmentCDC, CDC, EPA
National Primary Drinking Water Regulations List of Contaminants

Giardia lamblia is a microscopic parasite that causes giardiasis, a diarrheal illness affecting humans and animals in various parts of the world. The parasite forms environmentally resistant cysts that enable it to survive outside the host for extended periods, increasing the risk of contamination in drinking water sources. Ingestion of contaminated water containing as few as 10 cysts can lead to infection, highlighting the importance of ensuring safe drinking water supplies.

One way Giardia lamblia can enter drinking water is through the feces of infected humans or animals, which often contaminate water sources such as rivers, lakes, and wells. Additionally, Giardia cysts have been shown to attach and persist in drinking water biofilms, further increasing the risk of contamination. Therefore, proper treatment and monitoring of water sources are essential for preventing the presence of this parasite in drinking water.

Drinking water treatment processes, including filtration and disinfection, have been designed to effectively remove or inactivate Cryptosporidium parvum and Giardia lamblia. However, continuous efforts should be made by water utilities worldwide to develop and implement strategies for enhancing the effectiveness and efficiency of these processes, to minimize the occurrence of giardiasis outbreaks and protect the health of the population.

Giardia Lamblia in Drinking Water

Giardia lamblia is a waterborne parasite that causes a diarrheal illness called giardiasis. This parasite can be found in various water sources such as lakes, rivers, and drinking water supplies. Drinking contaminated water exposes individuals to the risk of infection.

In a study on the presence of Giardia cysts and Cryptosporidium oocysts in drinking water supplies in Northern Spain, it was found that 26.8% of tap water samples from municipalities with chlorination treatment contained Giardia cysts. This indicates the potential risk of infection from drinking water, even when it has undergone treatment.

The Environmental Protection Agency (EPA) has implemented guidelines for water treatment plants to monitor and remove Giardia lamblia from drinking water. These guidelines focus on processes such as filtration and proper disinfection. Some of the recommended methods for removing Giardia cysts include:

  • Coagulation and sedimentation
  • Granular media filtration
  • Ultraviolet (UV) light disinfection
  • Ozone disinfection
  • Boiling

However, the effectiveness of these methods may vary depending on factors such as water quality, temperature, and the presence of other contaminants.

In addition to tap water, Giardia lamblia can also be found in natural water sources, like lakes and rivers. A two-year monitoring study of a recreational and drinking water reservoir revealed the presence of Giardia cysts in  the reservoir, which was used for recreational purposes. However, the study found no trace of giardia cysts in the drinking water supply after a treatment facility processed the water. These findings highlight the importance of proper water treatment to ensure the safety of drinking water.

In conclusion, the presence of Giardia lamblia in drinking water is a significant concern. Ensuring proper water treatment and disinfection can help reduce the risk of infection. It is crucial for municipalities, water treatment facilities, and individuals to be vigilant about the quality of the water they consume and use for recreational purposes.

How to Test for Giardia Lamblia in Drinking Water

Testing for Giardia lamblia in drinking water is essential for maintaining water quality and ensuring the health of consumers. Various methods are employed to detect the presence of this harmful parasite in water supplies.

One common method for testing the presence of Giardia cysts in drinking water is the EPA Method 1623. This method involves three primary steps:

  1. Sample collection and concentration: A large volume of water (10 to 100 liters) is collected and then filtered through a sample concentration process to obtain a smaller, concentrated sample containing suspended particles, including potential Giardia cysts.
  2. Immunomagnetic separation (IMS): The concentrated sample is subjected to IMS, a process that uses magnetic beads coated with antibodies specific to Giardia lamblia. The beads bind to the cysts, allowing them to be separated from other debris in the sample.
  3. Microscopic enumeration: The separated cysts are stained with fluorescent antibodies, making them visible under a fluorescent microscope. Enumeration of cysts is conducted to determine the level of contamination in the water sample.

It is essential to continuously monitor and test drinking water quality to ensure the absence of Giardia lamblia and to maintain public health. Strategies for limiting Giardia contamination in water sources include source water protection, effective water treatment processes, and regular monitoring to detect any potential breaches in water quality.

How to Remove Giardia Lamblia from Drinking Water

Boiling Water

Boiling water is a simple and effective method for eliminating Giardia lamblia from drinking water. Bring water to a rolling boil for at least 1 minute to ensure that any cysts present are killed. It is important to remember that boiling will not remove other contaminants that may be present in the water.

UV Light Treatment

Using ultraviolet (UV) light treatment can be effective in deactivating Giardia lamblia cysts in drinking water. UV light disrupts the genetic material of the cysts, preventing them from reproducing. However, this method requires a properly functioning UV system that can maintain adequate UV intensity to ensure effective treatment.


Microfiltration can remove Giardia lamblia cysts from drinking water by physically trapping them in a filter with a pore size of 1-10 microns. The effectiveness of microfiltration depends on the quality of the filter and regular maintenance to prevent clogging.


Ultrafiltration uses a filter with pore sizes of 0.01-0.1 microns which can effectively remove Giardia lamblia cysts from drinking water. Similar to microfiltration, the efficiency of ultrafiltration depends on filter quality and maintenance.


Nanofiltration employs membranes with even smaller pore sizes (0.001-0.01 microns) to filter out Giardia lamblia cysts from drinking water. This method can also remove other contaminants such as heavy metals and organic molecules.

Reverse Osmosis System

A reverse osmosis system forces water through a semi-permeable membrane, which can remove Giardia lamblia cysts as well as other contaminants. These systems can be costly and require regular maintenance to keep them functioning efficiently.


Distillation involves heating water until it evaporates into steam, then condensing the steam back into liquid form. This process can effectively remove Giardia lamblia cysts and other impurities from drinking water. However, distillation requires a significant amount of energy and may not be an economical option for all households.


While chlorination can be effective in killing some microorganisms in drinking water, it is less effective against Giardia lamblia cysts. These cysts are resistant to typical chlorine concentrations used in water treatment; therefore, relying solely on chlorination may not be sufficient to remove Giardia lamblia from drinking water.

Ozone Treatment

Ozone treatment can be an effective method for inactivating Giardia lamblia cysts in drinking water. Ozone is a powerful oxidizing agent that can break down the cyst walls and render them harmless. However, ozone treatment systems can be expensive and may not be a practical solution for all individual households.

How Does Giardia Lamblia Get into Drinking Water

Giardia lamblia, a microscopic parasite, causes an intestinal infection called giardiasis. It primarily enters drinking water sources through contact with feces from infected people or animals. Contamination typically occurs when the parasites find their way into watersheds, which are areas of land that collect and store water for public use.

The most common pathway for Giardia to enter drinking water is through surface water. Streams, rivers, and lakes can become contaminated with Giardia cysts when sewage, animal waste, or feces from infected wildlife enters the water. Heavy rainfall and agricultural runoff can exacerbate this issue, increasing the likelihood of Giardia cysts being present in these water sources.

Watershed protection is essential in preventing Giardia contamination in drinking water. Strategies to protect watersheds include:

  • Restricting land use and activities near water sources to minimize the risk of human or animal fecal contamination
  • Implementing proper sanitation practices in recreational areas and campgrounds near water sources
  • Managing agricultural activities, such as livestock grazing and crop farming, to reduce runoff into water sources

In addition to watershed protection, proper treatment of surface water is crucial in reducing Giardia contamination. The Surface Water Treatment Rules (SWTRs), established by the United States Environmental Protection Agency (EPA), set forth guidelines for water treatment facilities to follow to ensure safe drinking water. Key components of the SWTRs meant to reduce biological contaminants include:

  • Filtration: Water treatment plants must use filtration methods, such as sand or membrane filtration, to physically remove pathogens like Giardia lamblia.
  • Disinfection: The use of chemicals like ozone or ultraviolet (UV) light helps kill or inactivate parasites to further reduce the risk of waterborne illness.

Giardia can also be transmitted through other means, such as recreational water facilities like swimming pools, where contaminated feces can come into contact with the water. In these instances, maintaining proper disinfection levels and practicing good personal hygiene can help minimize the risk of infection.

In summary, Giardia lamblia enters drinking water sources mainly through fecal contamination from people, animals, and the environment. Protection of watersheds and adherence to the SWTRs can significantly reduce the presence of Giardia in drinking water.

Effects of Giardia Lamblia on the Human Body

Giardia lamblia, a common parasite, poses a threat to safe drinking water worldwide. When individuals swallow water contaminated with this parasite, it can lead to gastrointestinal illness and other adverse health effects. In particular, swimming pools and travel to areas with inadequate water treatment systems can increase the risk of exposure.

Upon entering the human body, Giardia lamblia latches onto the small intestine’s lining. The ensuing infection can result in a range of symptoms, including nausea, weight loss, and dehydration. These symptoms often become more severe in children, as their immune systems are still developing.

Moreover, the parasite can cause malnutrition, as it disrupts the body’s ability to properly absorb nutrients. In severe cases, this malnutrition may lead to long-term health issues or complications. Addressing the infestation often requires medication to eliminate the parasite and alleviate associated symptoms.

Prevention is key to protecting oneself from Giardia lamblia. Strategies to reduce exposure include:

  • Ensuring access to clean and safe drinking water
  • Avoiding swallowing water when swimming in pools, lakes, or streams
  • Being cautious while traveling to areas with potentially unsafe water sources

In summary, Giardia lamblia is a harmful parasite that poses significant risks to human health. Understanding its effects on the body and implementing prevention strategies are critical to reducing the prevalence of infection and promoting overall well-being.


Giardia lamblia is a common waterborne parasite that can be found in various sources of drinking water. It has been detected in raw and treated drinking water worldwide and poses a potential health risk to those who consume contaminated water. The presence of Giardia cysts in drinking water supplies has been identified in northern Spain and other locations around Europe, further emphasizing the importance of addressing this issue.

Effective water treatment processes are crucial for reducing the risk of Giardia infection. Research has shown that conventional drinking water treatment facilities can help in lowering the concentrations of Giardia cysts. Disinfection methods, such as ozone and ultraviolet (UV) light treatment, can also aid in the removal or inactivation of the cysts. However, these approaches may not always be sufficient on their own.

To ensure the safety of drinking water, monitoring and maintaining water quality is essential. It is recommended that water treatment facilities regularly test water samples for the presence of Giardia cysts and other contaminants. Additionally, public health officials and policymakers should work together to establish guidelines and action levels for acceptable concentrations of Giardia in drinking water.

In the face of potential risks associated with Giardia in drinking water, individuals can take steps to protect themselves by using appropriate filtration or purification methods at home, such as boiling water or using certified water filters. Educating the public about the importance of safe drinking water and the risks posed by Giardia lamblia can also contribute to preventing infections and maintaining overall public health.

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