Common public drinking water contaminants in the USA

Latest update: Fall 2021

Here are the most common drinking water contaminants in water from public systems across the US. For those on well water, here are the most common well water contaminants.

While many of the risks to water taste and safety vary across different parts of the country, there are several leading threats to water quality that affect nearly all homes on public water in 2022.


In this article, we'll describe every common tap water contaminant, including:

  • Contaminant severity,
  • Effects on water quality,
  • Potential health consequences, and
  • How to identify and filter the contaminant.

Choose a contaminant category to find out more...

Why are these things in my water?

Soldotna company settles with EPA for $130,000 | Peninsula Clarion

Water is the earth's natural solvent, which means there are almost always substances dissolved within it.

As humans have transformed the environment, however, the variety and quantity of these contaminants have changed dramatically.

Even after our water is disinfected and filtered by public treatment plants, small amounts of dissolved contaminants can remain.

This is for two main reasons. This first reason is that removing all contaminant traces from water requires expensive filtering technology that isn't supported by our national infrastructure. The second reason is that many contaminants can be reduced to safe levels without the need to entirely remove them.

How are water contaminants managed?

Because they're so widespread, the federal Environmental Protection Agency has opted to set "Safe Limits" for contaminants rather than requiring them to be entirely removed from the water supply. These limits are based on large amounts of data and reviewed over time, and can be achieved with widely available filtration methods such as chlorination.

As a result, our municipal water plants aren't designed to produce contaminant-free water—instead, they aim to reduce the presence of over 90 different substances as required by the EPA’s Safe Water Act.

Private water sources, like well water, are not treated before usage. For those relying on these water sources, a dedicated well water filtration system is highly recommended.

How can I protect my home and family?

To improve the quality of your tap water beyond the EPA's safe drinking water limits, and protect against other potential impurities and contaminants, you can filter your water at home using a range of easily available filtration media.

Chemical contaminants

Colorful Liquids in Laboratory Glasswares

Chemicals are the most widespread contaminants in our drinking water—with some presenting an unknown risk to health.

Thankfully, they're also among the easiest and cheapest substances to filter.

Chlorine & Chloramines

Chlorine is the most noticeable contaminant in our drinking water due to its widespread use as a disinfectant agent. Traces of chlorine often remain in water that leaves treatment centers, causing a chemical or bleach-like taste and odor.

If plant matter (algae, dead leaves, etc) are present in the water supply during disinfection, chlorine can react with these materials to produce chemical byproducts. A common set of chlorine byproducts in tap water are trihalomethanes (THMs). While not thought to be harmful in small amounts, long-term exposure to these byproducts is linked to increased cases of cancer and birth delivery problems. In fact, THMs may play a role in some bladder cancers.

To reduce the risk of byproducts, many treatment plants have switched from chlorine-based agents to chloramines—a similar set of chemicals that a less reactive with plant matter.

Contaminant severity: Low. Increases with prolonged consumption.

Effects on water quality: Can cause chemical or bleach-like odors.

Potential health consequences: Increased risk of bladder cancer and infant birth delivery problems with high consumption.

How to identify Chlorine & Chloramines: A chemical smell. Check reports from your local water body.

How to filter Chlorine & Chloramines: Activated carbon filtration.


Another chemical that’s common in drinking water due to manmade reasons, fluoride has been added to US tap water for decades, in order to help prevent tooth decay. Up to one mg of fluoride per liter can be found in our water, although tiny amounts are also naturally present in the soil. According to the EPA, over 190 million Americans drink fluoridated water, with government agencies recently considering scaling back fluoridation programs, thanks to increasing levels of dental hygiene and the presence of fluorine in other consumer products.

Contaminant severity: None.

Effects on water quality: No taste, smell, or appearance.

Potential health consequences: May cause bone disorders if consumed at extreme levels, especially in children.

How to identify Fluoride: Water testing.

How to filter Fluoride: Reverse osmosis filtration.


Nitrogen is one of the earth’s most abundant elements, while nitrates are widely used in the production of crops and livestock. Organic nitrates appear in our tap water thanks to contamination from sewage. Inorganic nitrates are present due to runoff from fields sprayed with fertilizers. Hundreds of millions of pounds of nitrate-based fertilizers are spread across land in the US each year—especially in agriculturally-rich California—causing inevitable leaching into aquatic ecosystems.

Contaminant severity: Low at average levels.

Effects on water quality: No taste, smell, or appearance.

Potential health consequences: Prolonged consumption of high levels of nitrates is associated with nervous system and circulation disorders.

How to identify Nitrates: Water testing.

How to filter Nitrates: Reverse osmosis or anion exchange filtering.


Per- and polyfluoroalkyl substances (PFAS) are manmade chemicals that have gained recent attention due to discoveries about their widespread presence in the environment and our bodies. First used in the mid-twentieth century, PFAS and PFOS help form protective barriers in consumer and industrial products such as kitchenware, raincoats, and fire-extinguishing foam. While some PFAS chemicals have been phased out of production, many are still used, and all PFAS have extremely long lifespans. This means that they don’t break down once spilled into the environment, giving them the nickname “forever chemicals”. Scientists are currently researching the effects of PFAS pollution and consumption, with studies suggesting negative impacts on birth rates and fertility. 

Contaminant severity: Unknown. The long-term effects of PFAS are still being studied.

Effects on water quality: No taste, smell, or appearance.

Potential health consequences: Fertility, birth, and infant developmental issues. Hormone and thyroid disorders.

How to identify PFAS: Water testing.

How to filter PFAS: Activated carbon filtration or reverse osmosis filtration.

Pesticides & Herbicides

Pesticides are sprayed on crop fields and gardens, where they wash into rivers and lakes before making their way to public water reservoirs. In areas of the country with lots of agricultural activity, these chemicals can become concentrated, affecting biodiversity and aquatic life. While safe in low quantities, consuming small amounts of pesticides over many years can lead to bioaccumulation in the body and potential health disorders.

Contaminant severity: Low at average levels.

Effects on water quality: Unlikely to have any smell, taste, or appearance.

Potential health consequences: Long-term exposure/bioaccumulation may cause immunosuppression and hormone disorders.

How to identify Pesticides & Herbicides: Water testing.

How to filter Pesticides & Herbicides: Activated carbon filtration.


Pharmaceuticals are present in the water supply thanks to their widespread societal use, both for humans and in the livestock industry. This leads to drugs being thrown or flushed away, as well as excreted from our bodies. Surveys have found diphenhydramine, acetaminophen, and caffeine persisting throughout the environment, including in fish. Many pharmaceuticals can also pass through water treatment plants in tiny amounts—although these trace levels don’t have any recorded effect on the human body.

Contaminant severity: Low at average levels.

Effects on water quality: No taste, smell, or appearance.

Potential health consequences: Unlikely to cause any negative health effects.

How to identify Pharmaceuticals: Water testing.

How to filter Pharmaceuticals: Activated carbon or reverse osmosis filtration.


Sulfur is more of an issue in well water than in public systems, but it can still appear in municipal supplies, especially when water comes from a groundwater source. Here's how to remove sulfur from well water.

Even when levels of sulfur or hydrogen sulfides in water are high, no known health effects have been recorded. However, sulfur is well known for its “rotten egg” odor that can make water taste and smell off-putting.

Contaminant severity: None.

Effects on water quality: Can cause an unpleasant odor.

Potential health consequences: High levels may cause stomach upset in those who aren't accustomed to consuming sulfides.

How to identify Sulfur: Water odor.

How to filter Sulfur: KDF filtration or chlorination.

Volatile organic compounds

Volatile organic compounds (VOCs) are highly common chemicals that exist in the air, earth, and water, mostly due to urban and industrial pollution. VOCs are used in the production of cleaning products, paints, varnishes, and brake fluids, meaning that they’re present across society.

Contaminant severity: Low

Effects on water quality: Can cause earthy or fishy odors and tastes.

Potential health consequences: Prolonged consumption of VOCs are associated with the development of cancers, as well as damage to the circulatory and nervous systems.

How to identify VOCs: Water odor, water testing.

How to filter VOCs: Activated carbon filtration.

Metals & Minerals

While certain metals and minerals have no safe consumption level, others can be beneficial to water quality in certain amounts.

Depending upon the contaminant, a filter or a water softener may be more appropriate for reducing their levels.


Aluminum is a highly common element that exists naturally in the environment. While there may be some aluminum contamination caused by industrial pollution, most of the aluminum found in drinking water dissolves into the supply from groundwater aquifers, when water spends long periods underground. Long-term consumption of aluminum is may be associated with kidney diseases.

Contaminant severity: Low at average levels.

Effects on water quality: Usually none. Possible metallic taste.

Potential health consequences: Kidney issues after long-term consumption.

How to identify Aluminum: Water test.

How to filter Aluminum: Ion exchange or reverse osmosis filtration.


Arsenic is a heavy metal that’s especially prevalent in groundwater, where it can leach from the surrounding rock. It’s also a byproduct of certain industrial processes such as smelting and is used in some insecticides. Arsenic consumption is associated with digestive issues.

Contaminant severity: Medium.

Effects on water quality: No taste, odor, or appearance.

Potential health consequences: Kidney disorders, digestive issues.

How to identify Chlorine & Chloramines: Water testing.

How to filter Chlorine & Chloramines: Ion exchange or reverse osmosis filtration.

Calcium & Magnesium

Calcium and magnesium are found in tap water across most of the US, and are responsible for what’s commonly known as hard water. These minerals can give water a scratchy feel, stronger taste, and may cause scale to build on kitchenware and inside pipes. The presence of calcium and magnesium can also make it difficult to lather soaps.

Contaminant severity: None.

Effects on water quality: Can cause scale, water clouding, and stronger tastes (which many prefer).

Potential health consequences: May be beneficial to cardiovascular health in small amounts.

How to identify Calcium & Magnesium: Water appearance, smell, taste, and feel.

How to filter Calcium & Magnesium: Water softener.


Lead is a toxic metal, meaning that there is no safe consumption level. But lead can appear in tap water thanks to small naturally occurring amounts in soil, and more commonly from old corroding pipes. While the use of new lead piping is outlawed, many old lead pipes still exist across the country in older homes and buildings. If the pH level or temperature of a water supply changes, it can cause rapid corrosion of piping, which releases lead fragments. Lead can cause brain damage, kidneys disease, and nervous system disorders, and is especially dangerous to children.

Contaminant severity: High.

Effects on water quality: No taste or smell.

Potential health consequences: Nervous system, developmental, and kidney disorders.

How to identify Lead: Water testing.

How to filter Lead: Granular activated carbon filtration, reverse osmosis filtration.


Iron is a well-known water contaminant thanks to its recognizable orange coloring. Though it’s more of an issue in deep well water, areas of the US that have lots of naturally occurring iron in the soil may also have iron-contaminated public water. If you're on a well water source, here's how to remove iron if this is an issue you have noticed.

There are no recorded ill effects from drinking water that contains iron, but it can cause discoloration and poor tastes or smells. Like magnesium and calcium, iron can create scale buildups.

Contaminant severity: None.

Effects on water quality: Can cause discoloration, bad tastes, and odors.

Potential health consequences: None.

How to identify Iron: Water appearance and taste.

How to filter Iron: KDF filtration and sediment filtering.


Manganese is another scale-causing contaminant that naturally occurs in soil—although it’s also produced as a byproduct of mining and other heavy industries, as appears in common household products like batteries, glass, and cosmetics. When a high amount of manganese is present in tap water, it can cause aesthetic issues like clouding and staining, sometimes to the extent that water creates black rings in toilets and bathtubs.

Contaminant severity: Low.

Effects on water quality: Worsens water taste, causes staining of appliances and laundry.

Potential health consequences: High exposure to manganese has been associated with neurological issues in children.

How to identify Manganese: Look for staining and metallic tastes.

How to filter Manganese: Water softener.


File:Copepodkils.jpg - Wikimedia Commons

Most people on public water don't need to worry about bacterial or viral contamination, as dangerous pathogens are removed by disinfection.

Flooding, natural disasters, and isolated outbreaks can however cause microorganisms to appear in your tap supply.

Algae (cyanotoxins)

One of the biggest environmental issues currently facing lakes and rivers in the US is algal blooms. These huge accumulations of blue-green algae are caused by climate change and fertilizer pollution and cause stagnation as well as the release of cyanotoxins, excreted compounds that can cause skin and respiratory irritation. Most public treatment plants can effectively remove algae, but in sources suffering from algal blooms, cyanotoxins may remain in treated tap water.

Contaminant severity: Low.

Effects on water quality: Can worsen water taste.

Potential health consequences: Skin and respiratory irritation during algal bloom events.

How to identify Cyanotoxins: Earthy or musty tastes and smells, water testing.

How to filter Cyanotoxins: Activated carbon or reverse osmosis filtration.

Coliform bacteria

Coliform bacteria are a group of microorganisms whose presence is a sign that unsafe pathogens like E. Coli and unwanted substances like fecal matter may be present in the water supply. Coliform bacteria themselves are widespread throughout the environment and also exist in our bodies. They’re rarely detectable by taste and smell, but testing for them can help indicate overall water quality.

Contaminant severity: Low at average levels.

Effects on water quality: No effect on taste, smell, or appearance.

Potential health consequences: High levels of coliform bacteria suggest the presence of pathogens that can cause gastrointestinal distress and disease. 

How to identify Coliform bacteria: Water testing.

How to filter Coliform bacteria: Chlorination or UV purification.


Copepods are microscopic creatures that naturally live in freshwater. In areas of the country with purer water sources, copepods are more likely to appear in tap water, as they are more abundant in higher quality water, and that water requires less filtering. Copepods are not visible by eye and do not change water taste or appearance. They’re also safe to consume.

Contaminant severity: None.

Effects on water quality: No effect on taste, smell, or appearance.

Potential health consequences: None.

How to filter Copepods: Chlorination or UV purification.


While there are many common contaminants in municipal tap water, they usually appear in tiny quantities, and rarely present a serious threat to water quality or safety.

That said, it is possible to find dangerous substances like PFAS, lead, or cyanotoxins in your drinking water, even though it's been treated at a public plant. If you suspect that these or other substances are present in your water supply, you should get your water tested and use a relevant home filtration system to prevent future contamination.

The vast majority of Americans are far more likely to encounter safe substances that nonetheless worsen water taste, smell, and appearance—otherwise known as aesthetic contaminants. Simple filtration with activated carbon is enough to remove the majority of these compounds.