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Common Contaminants in Drinking Water: An Essential Guide

Drinking water is essential for human health and well-being, but it can also become contaminated with various substances that pose potential risks. Contaminants in drinking water can be classified into four main categories: physical, chemical, biological, and radiological. 

  • Physical contaminants are usually anything suspended in the water, such as soil from erosion.
  • Chemical contaminants are elements or compounds that can be naturally occurring or man-made, such as nitrogen, bleach, salts, pesticides, metals, and toxins produced by bacteria.
  • Biological contaminants are organisms in water, including microbes and microorganisms.
  • Radiological contaminants are anything that undergoes radioactive decay, such as uranium.

Numerous factors contribute to water contamination, and understanding these sources is crucial for preventing potential health issues. Some common sources of water contamination include fertilizers, pesticides, or other chemicals applied to land near the water source, industrial animal farms, manufacturing operations, sewer overflows, stormwater, and wildlife. Harmful germs and chemicals can cause various health complications, such as nausea, skin discoloration, organ damage, and even an increased risk of cancer.

To ensure the safety of drinking water, it is essential to implement measures to identify and limit the levels of contaminants. The National Primary Drinking Water Regulations (NPDWR) are legally enforceable primary standards and treatment techniques that apply to public water systems to protect public health. These regulations focus on limiting the concentrations of contaminants in drinking water, thus promoting safe and healthy drinking water for everyone. View a complete list here.

Sources of Contaminants

Natural Deposits

Contaminants in drinking water can often be traced back to natural deposits. Some common natural sources include nitrogen, arsenic, and toxins produced by bacteria. These substances can leach into groundwater, lakes, and rivers, which are often used as sources for drinking water supplies.

Human Activities

Human activities, such as mining, sewage disposal, and concentrated feeding operations (large industrial animal farms), can introduce a variety of harmful contaminants to drinking water sources. Mining operations can expose heavy metals previously buried underground, which can infiltrate local water supplies. Sewage overflows and improperly treated wastewater can introduce dangerous bacteria and chemicals into rivers and lakes, potentially compromising water quality.

Industrial and Agricultural Practices

Industrial and agricultural practices are significant contributors to drinking water contamination. Fertilizers, pesticides, and other chemicals applied to land near water sources can seep into groundwater or be carried into lakes and streams by rainfall runoff or snowmelt. Additionally, organics solvents, petroleum products, and heavy metals can migrate into aquifers, leading to further contamination issues.

Some specific contaminants resulting from these practices include:

  • Nitrate: Found in fertilizers, septic systems, animal feedlots, industrial waste, and food processing waste.
  • Pesticides: Applied to farmlands and other areas, pesticides can make their way into water supplies through runoff or seepage.
  • Metals: Released by various industrial activities, heavy metals like lead and mercury can contaminate water sources and pose serious health risks.

By understanding the common sources of contaminants in drinking water, efforts can be made to mitigate their impacts and protect public health.

Types of Contaminants

Physical Contaminants

Physical contaminants, also known as turbidity, can be naturally occurring or caused by human activities. These contaminants primarily impact the appearance and clarity of the water. Examples include sediment, soil particles, and organic matter suspended in the water. Treatment methods include filtration through porous membranes to remove sediment.

Chemical Contaminants

Chemical contaminants can come from various sources, including industrial processes, agricultural activities, and human or animal pharmaceuticals. Some common chemical contaminants found in drinking water are metals, salts, and toxins produced by bacteria. These pollutants can pose risks to human health if consumed at elevated levels. Treatment methods to remove chemical contaminants include reverse osmosis, ultrafiltration, distillation, and ion exchange.

Biological Contaminants

Biological contaminants, also called microbiological contaminants, are living organisms found in water. These microbes can include protozoa, viruses, and bacteria that may cause waterborne diseases. Contaminants may enter the water supply through fecal contamination from humans or wildlife, sewer overflows, or stormwater runoff. Treatment methods for biological contaminants include reverse osmosis filtration, disinfection, distillation, and ultraviolet light.

Radiological Contaminants

Radiological contaminants, or radionuclides, are radioactive elements present in water. These contaminants can originate naturally from rock formations or human activities such as nuclear power production and mining operations. Common radiological contaminants in drinking water include uranium, radium, and radon. To remove radiological contaminants, treatment options like aeration and activated carbon filters can be implemented.

Common Contaminants and Health Effects


Lead is a common contaminant found in drinking water due to corrosion of plumbing materials. Exposure to lead can lead to serious health issues, especially in young children. Health effects from lead consumption include damage to the nervous system, decreased red and white blood cell production, and impaired cognitive function.


Arsenic is a naturally occurring substance that can contaminate drinking water. Long-term exposure to arsenic in drinking water can cause cancer as well as liver, kidney, and reproductive difficulties. It can also cause skin discoloration and a sensation of “pins and needles” in the hands and feet.


Nitrate contamination can occur from sources like fertilizers and concentrated feeding operations. High nitrate levels in the water can be linked to a condition known as blue baby syndrome, which causes a decreased ability of the blood to carry oxygen and can lead to life-threatening organ and tissue damage in infants.


Copper contamination can happen due to copper pipes or pollution from mining, farming, or industrial operations. Ingesting high levels of copper can cause nausea, vomiting, and damage to blood vessels. Additionally, long-term exposure to copper can result in kidney and liver damage.

Bacteria and Viruses

Bacteria and viruses can enter drinking water through many different pathways, including stormwater runoff, sewage overflows, and wildlife. Exposure to these microbes can cause gastrointestinal issues, headaches, and other flu-like symptoms.


Parasites, such as Giardia and Cryptosporidium, can contaminate the water and cause illnesses. Symptoms of parasitic infections range from mild to severe and can include diarrhea, abdominal cramps, and dehydration.

Disinfection Byproducts

Disinfection byproducts (DBPs) are formed when disinfectants, like chlorine, react with organic materials in the water. Trihalomethanes are a common group of DBPs. Long-term exposure to these byproducts can increase the risk of cancer and cause liver, kidney, or nervous system problems.

Waterborne Diseases

Cryptosporidium and Giardia

Cryptosporidium and Giardia are protozoan parasites commonly found in contaminated water. These parasites can cause gastrointestinal illnesses such as diarrhea, cramps and nausea. They are often transmitted through ingestion of contaminated water or contact with contaminated surfaces.

Both parasites are resistant to chlorine disinfection, making it crucial for water treatment plants to incorporate additional purification methods, such as the use of ultraviolet light or ozone treatment. The CDC asserts that by boiling water for one minute, or three minutes if you’re at altitudes above 6,500 feet, these parasites can be successfully eliminated from potable water.

E. Coli and Coliform Bacteria

E. Coli and coliform bacteria are another common source of waterborne illnesses. These bacteria often originate from human or animal feces that contaminate water supplies through sewage overflows, faulty sewage systems, or polluted storm water runoff. Illnesses caused by E. Coli and coliform bacteria may include diarrhea, abdominal cramps, and fever.

Proper water treatment processes, such as chlorination, can effectively eliminate these bacteria from drinking water. The CDC also recommends boiling the water for 1 minute for these as well.


Typhoid is a bacterial infection caused by Salmonella typhi, which can be transmitted through contaminated water or food. Symptoms of typhoid include fever, fatigue, stomach pains, and sometimes a rash. The disease can be treated with antibiotics, but it is crucial to maintain the quality of drinking water to prevent typhoid outbreaks. The World Health Organization has projected that around 485,000 deaths due to diarrhea annually can be attributed to polluted water.


Cholera is an acute diarrheal illness caused by the bacterium Vibrio cholerae. This disease can lead to severe dehydration and even death if left untreated. Cholera spreads through the ingestion of water or food contaminated with the bacteria, often originating from human feces. Ensuring access to safe drinking water and proper sanitation practices are key to preventing cholera outbreaks.


Hepatitis A is a viral liver disease that can be transmitted through the consumption of contaminated water or food. Symptoms include fatigue, fever, jaundice, and abdominal pain. Vaccination against hepatitis A and improvement of sanitation and water supply are crucial for reducing the risk of this infection.

In summary, waterborne diseases pose significant threats to human health, and the importance of maintaining clean drinking water cannot be overstated. By understanding the various contaminants and employing effective water treatment methods, we can significantly reduce the risk of these diseases and protect public health.

Contaminants in Private Wells

Sources of Contamination

Private wells can be susceptible to various types of contaminants, including microbiological and chemical substances. Some common contaminants that can be present in private wells come from groundwater movement, surface water seepage, and runoff.

Heavy metals such as arsenic, antimony, cadmium, chromium, copper, lead, and selenium are among the contaminants found in private wells, posing risks like acute and chronic toxicity, liver, kidney, and intestinal damage, anemia, and cancer. Additionally, biological pollutants like microorganisms and microbes can cause health complications, such as gastro-intestinal distress or skin discoloration, if ingested.


professional water testing

Regular testing is essential for private well owners to ensure the water from their well is safe for consumption. The frequency of testing depends on the well’s location, nearby land uses, and potential contaminants that could affect the groundwater. In general, it’s advised to test your private well for contaminants annually, in the spring if possible, but higher frequency tests may be necessary if there’s a risk of contamination from a specific source or concern about a particular contaminant.


If contaminants are detected, homeowners should consider various treatment options based on the type and levels of contaminants present. For example, removing lead sources may involve replacing lead pipes or upgrading brass fixtures in private wells. Treatment methods for heavy metals can include reverse osmosis, ion exchange, or adsorption while biological contaminants may be managed through boiling, chlorination or ultraviolet disinfection.

By understanding the sources of contamination, regularly testing, and treating the water if necessary, private well owners can play an active role in ensuring their drinking water is safe and free of harmful contaminants.

Treatment and Filtration Methods


Disinfection is a crucial step in the water treatment process, aiming to remove harmful pathogens from drinking water. Common disinfection methods include the use of chemicals like chlorine and ozone, as well as ultraviolet (UV) light. Chlorine is one of the most widely used disinfectants worldwide for its efficacy in killing bacteria, viruses, and other harmful microorganisms. Ozone, on the other hand, offers a strong oxidizing agent capable of breaking down contaminants in water. Lastly, UV light provides a chemical-free method targeting the DNA of microorganisms, rendering them incapable of reproduction.

Reverse Osmosis

Reverse osmosis (RO) is a water filtering technique that employs a semipermeable membrane to remove impurities, such as dissolved salts, organic compounds, and ions, from water. RO systems work by applying pressure to the water to force it through the membrane, with contaminants being trapped and held back. This process results in high-quality, purified water suitable for consumption and various applications.


Distillation is a water purification method that relies on boiling water to separate contaminants based on their different boiling points. As water boils, it turns into steam, leaving behind impurities such as heavy metals, salts, and most chemicals. The steam then gets condensed back to liquid form, producing purified water. While distillation is effective in removing many impurities, it may not eliminate some volatile organic compounds (VOCs) that have boiling points similar to water.


Filtration is a common treatment method used by public water systems to remove suspended particles, bacteria, and other contaminants from water. This process is typically the final stage of a series of steps:

  • Coagulation: Chemicals are added to the water to cause small particles to stick together, forming larger particles, called flocs.
  • Flocculation: Gentle mixing is employed to encourage floc formation and growth.
  • Sedimentation: Gravity helps the formed flocs to settle at the bottom of the treatment tank, separating them from the water.
  • Filtration: The water then passes through filters, often made from sand or activated carbon, to remove the remaining particles and contaminants.

Each of these steps contributes to the overall effectiveness of the filtration process in producing safe, clean drinking water.

Regulations and Guidelines

Safe Drinking Water Act

The Safe Drinking Water Act (SDWA) is a federal law that was enacted in 1974 to protect public drinking water supplies in the United States. The SDWA authorizes the Environmental Protection Agency (EPA) to set national standards for drinking water quality to ensure the safety of public water systems. The Act has been amended several times since its establishment, with significant updates in 1986 and 1996, to strengthen protections against waterborne contaminants.

Under the SDWA, the EPA sets enforceable standards called Maximum Contaminant Levels (MCLs) for various contaminants in drinking water. These standards are based on the best available technology and take into consideration the costs of treatment. In addition to MCLs, the EPA also sets non-enforceable guidelines called National Secondary Drinking Water Regulations (NSDWRs) that address aesthetic aspects of drinking water, such as taste, color, and odor. You can find more information about these regulations on the EPA’s website.

Environmental Protection Agency

The Environmental Protection Agency (EPA) plays a crucial role in ensuring safe drinking water in the United States. As mentioned earlier, the EPA is responsible for setting and enforcing national drinking water standards under the Safe Drinking Water Act. The EPA sets legal limits on over 90 contaminants in drinking water, including bacteria, viruses, chemicals, and other potential threats to human health. You can find a list of these contaminants and their respective limits on the EPA’s Drinking Water Contaminants page.

Apart from setting standards, the EPA also oversees the implementation of various programs aimed at protecting the source of drinking water, like watersheds and underground aquifers. This includes the development of strategies to prevent contamination and the identification of areas in need of special protection measures. The EPA works closely with state, local, and tribal governments, as well as with public water systems, to implement these regulations and ensure compliance.

In summary, the Safe Drinking Water Act and the Environmental Protection Agency play key roles in safeguarding the quality of drinking water in the United States by setting standards and implementing regulations that protect public health.

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