Drinking Water Contaminants Identified & Explained

Written by: James Smith

Updated: March 3, 2023

Drinking water contamination

What does the government really do to protect us from harmful tap water contaminants? And what are some of the contaminants that you should be aware of? We answer these questions and a whole lot more in our deep dive into drinking water contamination.

What’s a Drinking Water Contaminant?

Before we dig deep into water contaminant classifications, it’s crucial to define exactly what a contaminant is when it comes to drinking water.

The Safe Drinking Water Act passed by congress in 1974 (and updated periodically since) defines a contaminant to be anything other than a water molecule.

That means any substance harmful or harmless is considered a contaminant. That’s not actually a very helpful definition as all water can be expected to contain a small amount of something extra. This could be minerals for example which are perfectly healthy and taste great.

The key point here is that the existence of contaminants in water does not automatically indicate that the water presents a risk to health (according to the EPA). A distinction must be made, which can be a long and difficult process.


How are Drinking Water Contaminants Identified?

There are a few ways in which water contaminants that potentially pose a threat to health are identified. Here’s a breakdown of the most common methods:

  1. Public Water System Monitoring: Public water systems are required to regularly monitor (and report) their water for certain contaminants. This monitoring can help identify any issues with water quality and allow for prompt corrective action.
  2. Source water assessment: Source water assessments are conducted to identify potential sources of contamination that may affect the safety of drinking water supplies. These assessments take into account factors such as land use, geology, and hydrology.
  3. Water quality testing: Water quality testing can be conducted on individual private wells or other water sources to identify any contaminants that may be present.
  4. Epidemiological studies: Epidemiological studies can be used to identify associations between water quality and health outcomes, which can help identify potential contaminants.
  5. Emerging contaminant monitoring: Emerging contaminants are contaminants that are not yet regulated but may pose a potential risk to human health. Monitoring for emerging contaminants can help identify potential risks and inform regulatory decisions.
  6. Contaminant candidate list: The Contaminant Candidate List is a list of unregulated contaminants that may pose a potential risk to human health. The list is used to prioritize contaminants for further study and potential regulation.

It’s the Contaminant Candidate List (CCL) that is probably the most important method of contaminant detection as it involves the detection of new contaminants which are then periodically added to the Safe Drinking Water Act. There are always new contaminants being discovered so it’s a really important way to stay protected.


How Do We Decide if a Drinking Water Contaminant is Harmful?

Contaminants that are proposed by the CCL (a new list of contaminants up for review is published periodically, see the latest one here) are then studied in order to assess their threat to the public.

These studies involve finding out the ‘safe limits’ for consumption and the specific threat to health. For example, manganese is hazardous to our health in large concentrations and through inhalation.

Therefore, studies were commissioned and published in 2003 regarding possible new regulations for manganese in drinking water. It was found that manganese is present in around 55% of the nation’s ground water public water systems. But, just 3% of samples exceeded the threshold of 0.30 mg/L.

It was therefore decided not to regulate manganese and incorporate it into the Safe Drinking Water Act. The reasons were:

  1. There was no evidence to suggest that the oral intake of manganese at levels common to Western diets was harmful.
  2. Manganese is also an essential nutrient so a balance had to be found. Since levels were generally very low, the benefits were deemed to outweigh the dangers.
  3. Drinking water ingestion of manganese accounts for a very small proportion of our overall exposure to manganese.

If the frequency and amount of a contaminant are considered to be sufficient enough to pose a health risk then the EPA will commission a detailed risk assessment and enforce new regulations.

In regulating a new contaminant, the EPA sets a threshold contaminant level which must not be exceeded when delivered from a public water system to an American home. Breaching the limit would be a health hazard and a violation.


What are the Types of Drinking Water Contaminants?

The EPA classifies drinking water contaminants into four categories. It’s these four categories and their constituent offenders that we’re going to be looking at in this section.


1. Physical Water Contaminants

These are substances that can affect the physical properties of water but are not chemically or biologically active. Physical contaminants are typically large particles or materials that can be seen with the naked eye or with magnification.

Examples of physical water contaminants include:

  1. Sediment: This includes sand, soil, and other particles that are picked up by water as it flows over the ground.
  2. Debris: This includes leaves, twigs, and other organic materials that are carried along by water.
  3. Rust: This can occur when water comes into contact with iron or steel pipes.

Physical contaminants can be hazardous because they can clog pipes and filters, leading to reduced water flow and potential damage to water treatment systems.

Additionally, physical contaminants can create breeding grounds for bacteria and other microorganisms, which can lead to waterborne illnesses. Some physical contaminants can also cause unpleasant tastes, odors, or colors in the water, which can make it difficult or unappealing to drink.


2. Chemical Water Contaminants

These contaminants can be naturally occurring or man-made and can come from a variety of sources such as agricultural activities, industrial discharges, and household products.

Examples of chemical water contaminants include:

  1. Pesticides: These are used to control pests in agricultural and residential settings and can end up in drinking water sources through runoff or leaching.
  2. Heavy metals: These include lead, mercury, and arsenic, which can be present in drinking water due to industrial activities or naturally occurring geological formations.
  3. Disinfection byproducts: These are created when disinfectants, such as chlorine, react with organic matter in water.

Chemical water contaminants can be hazardous because they can cause a range of health problems, from acute effects such as gastrointestinal illness to chronic effects such as cancer, neurological damage, and developmental problems. They may also alter the taste, color, and odor of water, making it unpalatable.

To protect our drinking water from chemical contaminants, we can take several measures, such as:

  1. Proper disposal of household chemicals: We should dispose of household chemicals, such as cleaning agents, batteries, and paint, according to local regulations.
  2. Use of natural or organic products: We can reduce the amount of chemical contaminants in drinking water by using natural or organic products instead of chemical-based ones.
  3. Proper storage of chemicals: We should store chemicals in a safe and secure manner to prevent leaks and spills.
  4. Monitoring of drinking water sources: Regular monitoring of drinking water sources can help identify potential contamination and allow for prompt corrective action.
  5. Installation of home water treatment systems: Home water treatment systems can remove many chemical contaminants from drinking water, providing an extra layer of protection for our health.


3. Biological Water Contaminants

Also known as microbiological contaminants, these are living organisms that can be found in drinking water and pose a risk to human health. These organisms can come from human and animal waste, soil, and other sources.

Examples of biological water contaminants include:

  1. Bacteria: These microorganisms can cause illnesses such as diarrhea, dysentery, and cholera.
  2. Viruses: These are infectious agents that can cause illnesses such as hepatitis A, norovirus, and rotavirus.
  3. Protozoa: These are single-celled organisms that can cause illnesses such as giardiasis and cryptosporidiosis.
  4. Parasites: These are organisms that live on or within another organism and can cause illnesses such as trichomoniasis and schistosomiasis.

Biological water contaminants are hazardous because they can cause a range of health problems, from mild gastrointestinal illnesses to life-threatening diseases. In addition, they can multiply rapidly in water, making it difficult to control their spread.

To protect our drinking water from biological contaminants, there are several measures we can take:

  1. Proper disposal of human and animal waste: We should ensure that human and animal waste is properly disposed of to prevent it from contaminating water sources.
  2. Regular maintenance of septic systems: Septic systems should be regularly maintained to prevent leaks and malfunctions that could contaminate water sources.
  3. Protection of water sources: Water sources should be protected from contamination by ensuring that nearby land use activities are managed properly.
  4. Use of water treatment systems: Water treatment systems such as chlorination and UV disinfection can effectively remove biological contaminants from drinking water.
  5. Regular monitoring of drinking water sources: Regular monitoring of drinking water sources can help identify potential biological contamination and allow for prompt corrective action.


4. Radiological Water Contaminants

These are defined as chemical elements that can emit ionizing radiation (dues to unstable atoms), which can be harmful to human health. These elements can occur naturally in the environment or be released through human activities such as mining and nuclear power production.

Examples of radiological water contaminants include:

  1. Cesium-137: This is a radioactive isotope that can cause cancer and other health problems.
  2. Uranium: This is a naturally occurring radioactive element that can cause kidney damage and other health problems.
  3. Radon: This is a naturally occurring gas that can accumulate in homes and other buildings and cause lung cancer.

Radiological water contaminants are hazardous because exposure to ionizing radiation can damage human cells, leading to radiation sickness, cancer, and other health problems.

We can safeguard our drinking water from radiological contaminants in a number of ways:

  1. Monitoring of water sources: Regular monitoring of drinking water sources for radiological contaminants can help identify potential risks and allow for prompt corrective action.
  2. Water treatment: Certain water treatment technologies, such as reverse osmosis and distillation, can effectively remove radiological contaminants from drinking water.
  3. Proper waste disposal: Proper disposal of radioactive waste from nuclear power plants and other sources can help prevent contamination of water sources.
  4. Regulatory controls: Government agencies can set and enforce standards for safe levels of radiological contaminants in drinking water to protect public health.
  5. Education: Education and awareness programs can help individuals and communities understand the risks of radiological contamination and take appropriate measures to protect themselves and their drinking water sources.


About the Author James Smith

James is the chief water geek here at His mission is to empower the consumer and allow people to take control of their health. His passion for water health is contagious, hopefully unlike your tap water!

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