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15 Common Water Contaminants & Their Potential Risks

Scott Winfield
Written by Scott Winfield
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Water contamination is very common in the US for many reasons. Some of the most frequently found contaminants in US drinking water include lead, arsenic, and pesticides. Although some contaminants carry little risk, others can lead to serious health issues when consumed.

15 Common Water Contaminants & Their Potential Risks

In this guide, we discuss 15 common water contaminants that may be lurking in your home’s water supply. We also cover the potential health issues they can cause and give you some tips on how to remove them.

Types of Drinking Water Contaminants

Types of Drinking Water Contaminants
Types of Drinking Water Contaminants

According to the Environmental Protection Agency, water-polluting substances fit into four distinct categories. Each subgroup of pollutants affects the physical and chemical properties of water differently, so knowing them will help you identify waterborne threats.

Let’s briefly describe each group and how to recognize them.

1. Physical Pollutants

Physical contaminants primarily refer to pollution caused by rocks and sediments in water. These impurities cause visible changes in color, opacity, and texture in liquids. As a result, they’re usually the most obviously recognizable pollutants.

Physical contaminants are extremely common in freshwater bodies where soil erosion happens often. Still, water bodies such as large lakes dissolve organisms over time, creating sediment-like materials that pollute water. Drinking still water from lakes or other areas can be dangerous due to pollutants of all kinds.

Water pipelines rarely have trouble with physical pollutants. However, in some cases, the groundwater delivered to households can become contaminated by sediments.

It’s more common to encounter physical impurities in above-ground sources. In general, the more quickly a stream or river moves, the fewer physical contaminants it has.

Thankfully, unlike other types of water contaminants, physical impurities are not especially dangerous in small quantities. However, a buildup in freshwater sources can kill organisms, creating even more harmful substances in water.

2. Chemical Pollutants

Chemical contaminants are among the most abundant impurities in water sources, and they can be both natural and man-made. They don’t alter the characteristics of water as noticeably as physical pollutants.

Natural chemical pollutants include nitrogen, arsenic, and toxins produced by bacteria. They’re often byproducts of runoff, erosion, or organisms within water. These chemicals usually seep into groundwater in small amounts, but they can cause serious health complications through continual exposure and ingestion.

Man-made chemical pollutants include bleach, pesticides, and the corrosion of lead and copper pipelines. Sometimes, these impurities come from improper disposal of chemical wastes like copper sulfate, which are used for pest control and gardening. Soil erosion moves harmful pollutants through streams and into groundwater, contaminating reservoirs.

Chemical pollutants in water can cause several health issues, such as nausea, skin discoloration, or worse. In extreme circumstances, the constant consumption of chemical impurities can cause organ damage and increase the risk of cancer.

3. Biological Pollutants

Biological contaminants include microorganisms and microbes, which include bacteria, protozoa, viruses, and parasites. Most of them are microscopic unless they amass themselves in colonies. Microbes are responsible for waterborne illnesses like cholera and typhoid fever.

Biological pollutants occur in both surface water and groundwater. Water treatment plants use chemicals and filtration to remove as many microbes as possible, but certain kinds are resistant to chlorine treatment. The main symptom of microbial infection is diarrhea, but nausea, vomiting, and other complications may also arise.

Most biological contaminants fester in waters that contain large amounts of human or animal feces. Faulty sewage treatment, overflowing waste management systems, and broken aquifers are often responsible for this. Treatment and filtration are the best ways of removing biological pollutants from water.

4. Radiological Pollutants

Radiological components comprise the last category of water contaminants. Almost any ionized chemical can be radioactive, but certain elements like cesium are the most common.

Just like arsenic, some elements from rocks called radionuclides erode through rivers over time, polluting groundwater sources.

Similar to chemical contaminants, radiological ones are both naturally occurring and man-made. Improper disposal of radiological wastes, broken reactors, or nuclear fallout can contaminate a water supply with radiological pollutants.

Once these pollutants fester in a water supply, they harm the aquatic environment, creating more impurities through death and decomposition.

Radioactive elements are closely linked to serious health complications, including cancers, and they’re impossible to spot with the naked eye. Fortunately, radiological pollutants are the least common contaminants found in drinking water.

15 Most Common Water Contaminants

With the four broad categories in mind, let’s take a look at the 15 most common water contaminants. Where applicable, we’ll mention ways to identify them and tell you how to protect yourself from repeated exposure.

1. Silt

Silt in Water
Silt in water

Silt is a catch-all term for bodies of suspended geological particles in water. It’s a physical contaminant made up of rock and sand particles. The main identifying characteristic of silt in water is turbidity or clouding.

While silt is a contaminant, it’s not dangerous to consume via drinking water. Still, it can make water unpalatable and unappealing. Most water sources contain small amounts of clay or silt, but you should still avoid any drinking source that looks turbid.

If your drinking water is particularly turbid, it will require extensive filtration over a long timeframe to improve its transparency.

2. Iron

Water with high iron content
Water with high iron content

Like silt, iron is considered a secondary contaminant. Iron occurs naturally in water, as it’s carried by rain and erosion. It muddies the water and makes it taste unpalatable, but under normal conditions, it doesn’t harm the human body.

While one kind is soluble and dissolves completely in water, insoluble iron can cause secondary complications, such as bacterial growth, pipe clogging, and red stains on fixtures.

As with silt, extensive iron water treatment will improve the water’s clarity and taste.

3. Lead

Lead in Drinking Water
Lead in Drinking Water

Lead primarily enters water through plumbing pipes and structures. The EPA has been monitoring lead and copper levels in water since 1991 to prevent exposure risks. Areas with water of a higher natural acidity are at a greater risk of pipe corrosion, causing lead pollutants.

Ingesting lead in large quantities can be toxic, especially for children. That being said, bathing or showering in lead-contaminated water is fine as it doesn’t typically cause skin irritation.

Thankfully, using lead pipes in modern plumbing systems is no longer legal, but many cities still use their old, lead piping networks. As a result, lead contamination from piping is still a common issue.

Lead water contamination was the main cause of the infamous Flint water crisis in 2014.

4. Copper

Copper in Water
Copper in water

Similar to lead, copper is a toxic metal that enters water supplies primarily through pipes and home fixtures. It doesn’t cause health complications as serious as lead poisoning, but swallowing a large amount is still harmful. As with lead, areas with acidic water are at higher risk of copper contamination.

A working technique to reduce the risk of copper contamination is to let the faucet run for a few minutes before using any water. Doing this should flush out the built-up copper flakes, leaving you with purer water.

Needless to say, if you’re remodeling your kitchen or bathroom, avoid using copper and lead pipes or fixtures as a preventative measure.

5. Arsenic

Arsenic in Water
Arsenic in water

Arsenic is a chemical contaminant that exists in nature as a trace material in rocks and sediment. This pollutant can enter groundwater either naturally or due to human activity. Mining, pesticides, and animal feed are some man-made methods that can cause arsenic contamination in water sources.

Arsenic is commonly found in groundwater reservoirs across the United States. As of 2019, wells in over 25 states have tested positive for arsenic contamination. Unfortunately, it’s very hard to detect, as you can’t smell, taste, or see arsenic in tap water or groundwater.

The good news is that contractors test wells for arsenic after drilling. If they get a positive reading, they will apply water treatment methods to help filter out the pollutants over time.

6. Trihalomethanes (THMs)


Trihalomethanes are man-made chemical contaminants that occur when organic and decomposed matter reacts with chlorine water treatment. THMs evaporate out of water easily. but they can still be found in tap water. Unfortunately, since the chemicals are colorless, they’re impossible to detect.

Studies and tests are still underway to precisely determine the risks of THMs. However, many scientists agree that inhaling or ingesting them can increase your risk of various cancers.

The best way to remove THMs from your drinking water is to use a carbon filter or a reverse osmosis filter, which are both highly effective at reducing THMs. Look out for filters that are certified to NSF/ANSI Standard 53. This shows that the unit has been specifically tested for its ability to remove THMs from water.

7. Pesticides

Pesticides in water

Improper disposal and handling of agricultural pesticides, which exist in liquid, solid, and powdered forms, can contaminate groundwater. Pesticides are considered hazardous waste and should be properly disposed of by professionals.

While large volumes of pesticides in water can be deadly, the pesticide levels in drinking water are usually low. However, with enough exposure, you can experience symptoms like dizziness, numbness, and convulsions.

If you live in an agricultural area and encounter these issues, call the Poison Control Center immediately.

8. Nitrogen


Nitrogen is one of two prominent chemical nutrients that often pollute water sources. It mainly enters waterways through agricultural practices, namely the application of fertilizers.

A nitrogen buildup can cause hypoxia in water, damaging the environment and harming people who drink it.

Infants under 4 months are especially susceptible to an overabundance of nitrogen in water, as it can restrict oxygen transportation in their blood. High nitrogen levels are also linked to aquifer vulnerability, as this substance can easily seep into the groundwater to pollute it.

A nitrate water test is the quickest and most accurate way to identify nitrogen in your drinking water.

9. Phosphorus

Phosphorus in water

Phosphorus is another fertilizer element that can contaminate water. As with nitrogen, plants grow abundantly due to phosphoric buildups, causing eutrophication. Once they do, they consume a large amount of the water’s oxygen, killing fish and making the water harmful to drink.

Phosphorus in water doesn’t do much harm to humans by itself. However, it can encourage algal blooms to grow, many of which secrete toxins that harm people when ingested.

As a result, nitrogen and phosphorus make up a special group of nutrient pollutants. Farmers and agriculturists must ensure not to let these chemicals run off into the groundwater.

10. Fluoride

Fluoride in water

Fluoride is a “good” contaminant in many water sources across the country. Water authorities have purposely added fluoride to drinking supplies for dental health since the 1940s, as it’s been shown to strengthen enamel.

Over the years, concerns have been raised about the potential negative health effects of consuming fluoride via drinking water. For example, there have been mixed studies about potential links between fluoride and osteosarcoma, a kind of bone cancer.

However, most investigations have not found conclusive evidence. So, based on current knowledge, fluoride in water doesn’t cause harm to animals, plants, or human beings.

11. Giardia


Giardia is one of the most common microbial threats found in drinking water. It’s a parasite that lives in human and animal intestines. When it’s excreted, it enters a shell-like form called a cyst, which protects it until it’s ingested again.

Giardia enters water supplies through contaminated human and animal feces. Naturally, this means that giardia contamination is most common in agricultural areas.

The main symptoms of ingesting water contaminated with Giardia are long-lasting nausea and diarrhea, and infections are far more common in children than adults. Stagnant bodies of water like ponds and lakes are often contaminated with Giardia, but it’s also regularly found in domestic water supplies.

The best way to remove Giardia cysts from your drinking water is to use a filter system fitted with UV light, which neutralizes microorganisms. You can also use a filter with an absolute pore size of 1 micron or less to trap the cysts and prevent them from reaching your faucets.

12. E. coli

E. coli
Water contaminated with E. coli

Like Giardia, E. coli is a microbial threat that contaminates water via the stool of humans or animals. Rather than parasites, E. coli is a kind of bacteria. Most strains of the bacteria are harmless, but some can cause severe cramps and blood vomiting.

E.coli is very infectious, even in small amounts. As a result, consuming even a small amount of contaminated water can cause health issues in humans.

Fortunately, most public water sources are treated with chlorine to prevent E. coli outbreaks. Still, it’s important to stay vigilant and notify a doctor if you experience symptoms of E. Coli contamination, such as nausea and diarrhea.

13. Cryptosporidium (“Crypto”)

Cryptosporidium Water Test

The CDC lists cryptosporidium as a leading cause of waterborne infection in the United States. Also known as “Crypto,” this parasite is shed through stool and lives in human intestines, just like Giardia and E. coli.

Cryptosporidium parasites are commonly found in water because they’re resistant to chlorine. They can survive as many as ten days in treated water as cysts. Typically, Crypto infections only last a few weeks, but they can cause severe complications for people with weakened immune systems. As it’s resistant to chlorine, Crypto is often found in swimming pools and hot tub water.

14. Radium

Radium Water Test

Radium is one of the most common radiological pollutants found in water. It’s a naturally occurring element that forms when elements like thorium and uranium decay, which are both found in trace amounts in rocks and sands.

The dangers of radionuclides lie in their absorption. Fish, animals, and plants can absorb radium from water, and when it’s ingested by humans it can increase the risk of cancer.

Radium is impossible to detect without specialist equipment, as you can’t see, smell, or taste it. This is why public water systems are usually tested for radium before the water is distributed to people’s homes.

15. Radon

Water polluted with Radon

Chromium is often found in two forms in drinking water: Chromium-3 and Chromium-6. Chromium-3 occurs naturally and is an essential nutrient as it helps with fat and sugar metabolism. So, if your water contains small amounts of Chromium-3, this is actually a good thing.

Chromium-6, on the other hand, is much more concerning. Although it can also occur naturally, it’s often a byproduct of industrial processes such as leather tanning, chrome plating, and certain types of wood preservation.

If your drinking water contains high levels of Chromium-6, it can lead to an increased risk of lung and stomach cancer. Plus, it can cause dermatitis, respiratory problems, and issues with pregnancies.

Reverse osmosis systems are usually effective at removing Chromium-6. However, we recommend choosing a system that explicitly states it can remove this contaminant.

What Should You Do if You Drink Contaminated Water?

What Are the Health Effects of Drinking Contaminated Water

Unless you test the water before you drink it, you may only be able to tell it’s contaminated when you start experiencing unpleasant symptoms related to a specific contaminant. If this happens, contact a medical professional as soon as possible.

Symptoms caused by most contaminants usually don’t last very long and can be easily treated. However, some contaminants can pose more serious health risks.

In all cases, prevention is the best course of action. You should never drink from stagnant bodies of water, and you should regularly test your water at home to identify any contamination.

For more information about water contaminants, including uncommon and rare varieties, please consult the Environmental Protection Agency and the Center for Disease Control websites.

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Scott Winfield
Scott Winfield
My name is Scott Winfield and researching and writing about water filters and other strategies to purify water has become my full time passion in recent years. I'm glad that you found our site and you can look forward to authoritative and well researched content here to help you get the best in water.
    1. Hello Bobby, an easy way to test your water is using an at-home water test kit where we provide a link to a recommended kit. If you didn’t want to do it yourself and use a local business we have a recommended water system installer in your area, they are About Time Plumbing and Drain at 813-929-7778.

  1. In a recent broadcast we viewed on water contamination, PERFLUOROOCTANOIC ACID was discussed in detail. Is this a common contaminant in city water in Ventura, California?

    Thank you for your time, attention and response.

    1. Hi Lawrence, thank you for your question. The most definitive way to answer this question is to do a quick water test on your household water and see what’s in there. We have recommended water testing kits on our site, if you’d like to try one of those. That will give you the confidence on what is and isn’t in your water.

  2. It’s great that you talked about how it is important to learn, understand, and react to the causes and symptoms of polluted water. I saw an informercial on the TV last night and it gave some warnings about contaminated water. It is quite alarming, so maybe we should ask for water treatment services.

  3. I live in a condominium located in Palm Beach County. I have been told repeatedly that our pipes would be replaced, which we have recently been assessed for. No one has given me a start date, just the run around. The water that comes out of my faucets leave a pink/yellow slime and/or major soot buildup. It’s disgusting. AND I have pictures of the corroded piping behind the walls. My family has gotten eye infections and skin irritations since moving into this building. What can I do or what are some steps I can take so that I can create a sense of urgency in this matter? After having water tested, and what kind of testing, do I call the health dept or the EPA? Your advice is much needed, please and thank you!!!

    1. Hi Elle, I’m sorry to hear about the state of your water in your condo. It’s not clear if the replacement pipes you’re referring to is by your condo maintenance folks or if you’re talking about your local government and utility. I would escalate to a high level within your condo management organization to make sure this gets a higher priority. If it’s the local government or utility, I would make sure you have communicated with them and documented the issue with a formal complaint or filing. Here’s the information for the Palm Beach County water utility.

    1. Hi Jill, I would recommend looking at products we’ve reviewed that suit your needs and then you’ll see the capabilities of each that we reviewed. For example, if you’re thinking about an under-sink water filter or a whole-house water system, go to those reviews and you’ll see our results and recommendations.

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