5 Ways Water Can Be Contaminated

An explanation of the different types of contaminants that can appear in drinking water as categorized by the EPA and the best ways to purify each

Updated: June 24, 2023
Jeremiah Zac


The EPA defines “contaminant” as any physical, chemical, biological, or radiological particle present in the water supply—it’s a term often used broadly to identify anything other than the H20 water molecule.

While many contaminants are harmful if consumed at certain levels, some are naturally occurring elements found in rivers, lakes, and groundwater—some are harmless or even beneficial. Thus, it’s reasonable for drinking water to contain at least small amounts of contaminants.

Regulatory laws such as the Safe Drinking Water Act of 1974 set standard levels for each contaminant to be considered safe for human consumption. Harmful contaminants such as arsenic and Giardia have stricter standards than ones that pose less of a health risk such as magnesium and iron.

The reason it’s important to be familiar with the different types of contaminants is that not all contaminants can be purified through the same method—some require a more specific means of purification in order to be nullified safely. Therefore, knowing what types of contaminants are present in your water supply will provide a better understanding of which purification system best suits you.

While the EPA does have standards for municipal drinking water systems to protect citizens from some contaminants, it isn’t a guarantee that some won’t slip through, nor is it unwise to take full responsibility for the quality of your own water supply.

This article will look into the 5 ways water can be contaminated by dividing them up into categories and giving examples for each.

Physical contaminants

Physical contaminants in water are categorized as any particle that is non-chemical or non-biological in nature, and generally the largest types of contaminants.

Examples of Physical Contaminants

  • Sediment
  • Sand
  • Silt
  • Clay
  • Rust
  • Scale
  • Other Suspended Solids

The most common example of physical contamination is sediment, sand, or any organic material suspended in the water from nearby sources. This could include silt from the bottom of a riverbed, leaf fragments from overhanging vegetation, or even larger detritus resulting from human activity.

Potential Dangers

In low concentrations, physical contaminants can discolor the water and add an element of cloudiness or can impart a strange taste. In higher concentrations, physical contaminants can cause damage to piping and water infrastructure and can even pose a risk to human health if consumed regularly.

Microplastics, minute particles of plastic material, have also emerged as a substantial physical contaminant of late. Originating from an array of sources—everything from decomposed plastic waste to fibers shed from synthetic clothing during washing—they're alarmingly pervasive in the environment and have been found in the most remote corners of our planet.

Best Methods of Filtration

    Sediment Filters

    Sediment Filters are designed primarily to target physical contaminants, working on the principle of size exclusion to target larger particles. They act as sieves, allowing water to pass through while trapping sand, silt, or rust. These filters are typically the first line of defense in a multi-stage filtration system, protecting downstream filters from clogging up and helping enhance their longevity and performance.

    Sediment filters can be purchased as a standalone filter and used in conjunction with a larger filter system or might be pre-included as part of a complete whole-house filter system.

    Activated Carbon

    Activated Carbon Filters are designed to filter a wider range of contaminants in addition to physical contaminants. Through the process of adsorption, contaminants bind to the porous structure while water passes through.

    Activated carbon is particularly adept at removing chemicals and microorganisms much smaller than most physical contaminants. While it can catch some larger particles, it should ideally be used in conjunction with a sediment filter for best results.

    Reverse Osmosis

    Reverse Osmosis (RO) works by filtering contaminants at the molecular level. These systems use a semi-permeable membrane to remove up to 99% of dissolved salts, particles, organics, and other contaminants from water. While RO membranes themselves are certainly small enough to block any physical contaminant, RO systems typically contain a sediment pre-filter to block physical particles before they reach the membrane level.

    Chemical Contaminants

    Chemical contaminants are a category of water impurities that comprise a variety of substances, both natural and human-made, that can be harmful to human health when consumed beyond certain thresholds. In contrast to physical contaminants, these are typically dissolved in water and cannot be easily removed by basic filtration methods.

    Both surface water and groundwater systems can contain chemical contaminants of natural and man-made origin. Surface water is generally more susceptible to pollution from runoff carrying pesticides, herbicides, and industrial chemicals, while groundwater can often contain high concentrations of naturally occurring elements such as iron and manganese.

    Examples of Chemical Contaminants

    • Inorganic Compounds (IOCs)
    • Volatile Organic Compounds (VOCs)
    • Synthetic Organic Compounds (SOCs)
    • Pesticides
    • Herbicides
    • Industrial Chemicals
    • Pharmaceuticals

    Encompassing an array of substances from essential nutrients like calcium and magnesium to potentially harmful elements such as arsenic, lead, and mercury, Inorganic Compounds (IOCs) represent mineral-based compounds in our water systems, distinguished by their absence of the carbon element.

    Regulated by the Safe Drinking Water Act, which sets stringent standards to ensure public health, permissible levels of these compounds in our drinking water are scrupulously monitored.

    While the origin of some of these IOCs is naturally occurring—leached from the native soil and rock of water sources—others are a byproduct of human activities, such as those from agricultural and industrial undertakings, underscoring the complex landscape of our water supply's composition.

    Encompassing vast categories of carbon-based chemicals, Volatile Organic Compounds (VOCs) and Synthetic Organic Compounds (SOCs) present a diverse spectrum of substances in our water systems.

    VOCs, with representative compounds like benzene and toluene, are predominantly birthed from industrial processes and the utilization of petroleum-based products.

    SOCs cast a wide net, covering substances from agricultural pesticides and herbicides to industrial chemicals and even pharmaceuticals. Factors such as agricultural and industrial activities, coupled with improper disposal of substances, coalesce to steer these compounds into our water supply systems, further amplifying the intricate web of potential contaminants within our crucial water resources.

    Pesticides and herbicides are widespread in agricultural areas and can find their way into both surface and groundwater sources while industrial chemicals can come from an array of manufacturing processes and are typically more common in areas with a high density of industrial activity.

    Pharmaceuticals enter our water systems through human waste or the improper disposal of medications and can cause a wide range of unintended health consequences.

    Potential Dangers

    The health concerns related to chemical contaminants are wide-ranging, and often depend on the chemical itself and the concentration. Some contaminants like arsenic and certain VOCs are known carcinogens, while others like nitrates can cause health problems, particularly in infants and the elderly.

    Long-term exposure to even low levels of certain chemical contaminants can potentially lead to chronic health issues, which is a reason for the existence of regulatory standards in the Safe Drinking Water Act.

    Best Methods of Filtration

    Activated Carbon

    Activated carbon is especially adept at filtering harmful molecules due to the adsorption process, using its highly porous surface to trap them as the water passes through. This makes activated carbon filters one of the most widely used home purification systems for removing common chemical contaminants, particularly VOCs, SOCs, pesticides, herbicides, and pharmaceuticals. For most home situations, an activated carbon filter is more than adequate to provide safe, clean drinking water.

    Reverse Osmosis

    Reverse Osmosis systems take chemical filtration a step further by filtering at the molecular level, removing some chemical contaminants that carbon filters cannot, such as some inorganic compounds and elements. This makes RO systems ideal for water sources that contain more obscure substances such as some dissolved solids, fluoride, and nitrates.

    Biological Contaminants

    virus, bacteria, art

    Biological contaminants, sometimes referred to as microorganisms, constitute a significant category of waterborne pathogens that can cause diseases in humans, commonly categorized as protozoa, bacteria, and viruses.


    Protozoa are a type of single-celled parasite often found in surface water bodies and are the largest type of biological contaminant. With the ability to survive in harsh conditions due to a protective outer shell, protozoa often require more coarse measures to eliminate than other biological contaminants.

    Examples of protozoa are Giardia, often found in streams contaminated with animal feces, and Cryptosporidium, known to be highly resistant to disinfection methods that can cause gastrointestinal issues.


    Bacteria are single-celled microorganisms that thrive in a variety of specialized conditions, most commonly existing in regions of the world that have less stringent water quality standards. Common strains of waterborne bacteria are E. coli or Salmonella and are usually a result of fecal contamination that has been polluted by human or animal waste. Other common types of bacteria are Legionella, Shigella, and Cholera.


    Viruses are the smallest type of biological contaminant and can reproduce only inside the cells of a host organism. Waterborne viruses, such as the Norovirus, can make their way into water supplies from sewage overflows, poorly functioning wastewater treatment systems, or contaminated stormwater runoff.

    Potential Dangers

    Human consumption of water contaminated with microorganisms is of particular concern due to the high potential for dangerous and often, life-threatening illness. Symptoms can range from diarrhea and vomiting to fever and significant dehydration.

    Certain vulnerable populations, like the very young, elderly, or immunocompromised individuals, can experience more serious health impacts and even death. Thus, it's crucial to ensure that our water supply is appropriately treated to remove these harmful pathogens.

    Best Methods of Filtration

    UV Purification

    UV Purification, or Ultraviolet Purification, is an extremely effective method for eliminating the threat of waterborne diseases, using UV light to render microorganisms inactive. It does so by damaging the DNA of the pathogen, preventing it from reproducing, and therefore, removing the threat of infection. UV purification systems are often used in conjunction with a larger, whole-house purification system.

    Reverse Osmosis

    Reverse Osmosis systems are effective against biological contaminants due to the membrane. While viruses are extremely small, the semi-permeable membrane in an RO system has such small pores that even these microscopic pathogens are effectively kept out of your drinking water.

    Activated Carbon

    Activated Carbon Filtration can also be a line of defense against some forms of biological contaminants, specifically certain bacteria and protozoa. While it is not as effective against viruses, the porous nature of activated carbon provides a large surface area that can trap these larger microorganisms.

    Radiological Contaminants

    While less common than other forms of water contamination, radioactive isotopes, such as Radon, Alpha, Beta, Uranium, and Radium can present serious health risks when present in our water supply.

    Examples of Radiological Contaminants

    Radioactive isotopes (i.e. Radon, Alpha Beta, Uranium, Radium) occur naturally in the environment at very low levels, formed from the decay of unstable atomic nuclei over time, and are often found in both groundwater and surface water when leached from certain types of rock and soil. Human activities, such as mining or the use of nuclear power, can also contribute to the increase of these isotopes in our water supply.

    Potential dangers

    Higher levels of these radiological contaminants are dangerous because of the ionizing radiation they emit causing damage to cells and DNA, potentially leading to kidney damage or cancer.

    Best methods of filtration

    Ion exchange, reverse osmosis, and distillation are among the most effective methods for reducing levels of radioactive isotopes. Ion exchange systems work by swapping unwanted ions in the water with less harmful ones, while reverse osmosis uses a semi-permeable membrane to remove radioactive isotopes. Distillation, on the other hand, works by evaporating water and then condensing it back into a liquid, leaving contaminants behind.

    Conditional Factors

    While not technically considered a contaminant, water conditions can present certain unwanted factors in the water that may need further treatment.


    Total Dissolved Solids, or TDS, is a measure of the combined total of organic and inorganic substances contained in a liquid. This includes anything present in water other than the pure water molecules and encompasses a wide array of substances such as minerals, salts, metals, cations, anions, and other trace elements.

    While TDS itself is not necessarily harmful, the level of TDS can be a helpful indicator for further investigation of other contaminants. A low TDS level indicates that water is more pure, with fewer substances dissolved in it. Conversely, high TDS levels can indicate hard water or water that may have a significant presence of heavy metals, salts, or other potential contaminants.

    And while certain dissolved solids are harmful, some elements, such as calcium and magnesium, are beneficial for health in small amounts.

    TDS is measured by testing with a TDS meter or with test strips


    Water hardness is a measurement of certain dissolved solids that contribute to a “hardness” quality in the water, primarily calcium and magnesium.

    Water hardness itself doesn't pose a health risk; in fact, calcium and magnesium are essential dietary minerals. But high concentrations of hardness may cause functional problems to the water system if not treated.

    For example, it may cause scaling in pipes and on dishes, reduce the lathering ability of soaps and detergents, and shorten the lifespan of appliances like washing machines, dishwashers, and water heaters.

    Water hardness is treated with a water softener via ion exchange or a water conditioner.


    The pH level of water is a parameter that measures the balance between acidity and alkalinity. While pH itself does not necessarily pose a direct risk to human health, it can be an indicator of secondary issues.

    For example, low pH indicates acidity and can lead to leaching of metals, which can have health impacts. Additionally, the pH level of water has a direct effect on the effectiveness of other water filtration systems such as water softeners and iron filters.

    The Safe Drinking Water Act, while not mandating a specific range for pH, recommends a range between 6.5 and 8.5 as this minimizes the risk of water being corrosive or scaling.

    The pH level of water can be determined with a test meter or test strips.

    Temperature, color, taste, odor

    The most immediate method of determining the condition of water is by using our senses. Properties such as temperature, color, taste, and odor can often signal a problem that may need further investigation and water quality testing. Never neglect your senses!

    Thank you for taking the time to read our article on the 5 ways water can be contaminated. We'd love to hear your feedback in the comments section below. If you've found this article to be useful and are interested in learning more, be sure to sign up for our newsletter.

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    I'm Jeremiah, the owner of World Water Reserve. I'm a writer and researcher with a particular interest in sustainability and rural living, water scarcity, and innovative water purification methods. I utilize my multimedia and communication experience in the NGO and humanitarian fields to bring light to important topics. My passion is to educate others on the reality of the global water crisis and on ways to sustain themselves and their families in the midst of it.
    Jeremiah Zac