What is in Tap Water? 12 Common Contaminants Revealed

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Tap water isn’t s clean as it looks. Most drinking water supplies, including public water, contain traces of chlorine (or chloramine), fluoride, lead, VOCs, pesticides and herbicides, arsenic, and more. Some of these impurities have known health effects.

In this guide, I’ll be sharing the most common toxins in tap water. All water supplies differ, and I recommend testing your water to get an understanding of exactly what it contains.

Some of the most common contaminants in tap water are:

  • Chlorine
  • Chloramine
  • Fluoride
  • Lead
  • Arsenic
  • PFAS
  • Pharmaceuticals
  • VOCs
  • Pesticides & Herbicides
  • Nitrates
  • Methyl Tertiary Butyl Ether (MTBE)
  • Perchlorate

☢️ Common Toxins in Water


Chlorine is added to public water systems as a disinfectant. Chlorine prevents the growth of microorganisms like bacteria and viruses, making water safe to drink. However, chlorine has its own health effects. It can dry out hair and skin, and can give water an unpleasant taste and odor.

The safe level of chlorine is up to 4 mg/L.

municipal drinking water chlorination


Chloramine is formed when chlorine and ammonia react. This chemical is used by an increasing number of states as a disinfectant for public drinking water.

Chloramine has similar health effects to chlorine. It can also affect the taste and smell of water, and lasts longer in water, but is less reactive with organic materials.

Up to 4 mg per liter of chloramine is safe in drinking water.


Fluoride is a controversial impurity that the majority of states now add to their public drinking water supplies. Fluoride has proven oral health benefits, but it may also have long-term health effects.

According to federal regulations, public drinking water fluoride levels shouldn’t exceed 4 mg/L.


Lead is one of the most dangerous drinking water contaminants. This accumulative heavy metal can build up in the body over time, with devastating long-lasting effects.

Lead can get into water through old lead water supply pipes. Because of how harmful this contaminant is, the maximum contaminant level for lead in tap water is 0 mg/L .

Lead in faucet water.


Arsenic is a naturally occurring chemical element that leaches into ground water. This contaminant is most commonly found in well water supplies.

Arsenic is present in higher levels in certain states, such as Michigan. This chemical has been linked to heart disease, cancer, and ugh blood pressure.

The maximum quantity of arsenic in tap water is 0.01 mg/L.

arsenic in groundwater map
Source: United States Geological Survey (USGS.gov)


PFAS are a number of accumulative “forever chemicals” that were used widely in manufacturing before their dangers were known. PFAS linger in the environment for hundreds of years, and can cause developmental, reproductive, and immunological problems.

PFAS are known as emerging contaminants, and they don’t yet have an official maximum contaminant level. Most states set their own standards for PFAS in drinking water. The EPA’s non-enforceable advisory level for PFAS is 70 parts per trillion, or PPT.


Pharmaceuticals like antibiotics, antidepressants, steroids, and anti-inflammatories make their way into water supplies because of irresponsible waste disposal by humans. Our knowledge of the dangers and potential health impacts of pharmaceuticals is limited.

Pharmaceuticals are also classed as emerging contaminants, and there are no legal guidelines for these impurities at the moment.

Pharmaceutical medicines


Volatile organic compounds, otherwise known as VOCs, are toxic chemicals that can affect both the environment and human health. These chemicals may vaporize as gas in the air or leach into surface water supplies. Most VOCs end up in the ground, air, or water as a result of industrial pollution and poor waste disposal practices .

There are a variety of VOCs in existence today, some more prevalent than others. Benzene, methylene chloride, tetrachloroethylene and formaldehyde are all common VOCs that can make their way into drinking water supplies.

Each volatile organic compound is regulated by the EPA and has its own maximum contaminant level, depending on the risk it poses to human health.

Pesticides & Herbicides

Pesticides and herbicides get into water through surface runoff. These agricultural chemicals are present in higher quantities in areas with poor farming practices.

There are many different types of pesticides and herbicides, and not all have the same health effects. Depending on the type and quantity of the chemical you’re exposed to in drinking water, you may be at an increased risk of skin and eye irritation, cancer, nervous system damage, endocrine disruption, and more.

The recommended benchmarks for pesticides and herbicides depend on the exact chemical. There are around 50 pesticides alone that are known to cause health effects when consumed.

Farming tractor spraying agricultural chemicals.


Nitrates are molecules containing nitrogen and oxygen or ozone. All living things need nitrogen, but, at high levels, nitrates can be dangerous to health. Pregnant women and infants are especially at risk of the health effects of nitrates.

It’s common for nitrate to occur naturally in groundwater and surface water. However, this isn’t usually a cause for concern. High levels of nitrates are more often associated with poor well construction and improper farming practices, such as poor animal waste disposal and pesticide or herbicide overuse.

Drinking water containing less than 10 mg/L of nitrates is said to be safe to drink.

Methyl Tertiary Butyl Ether (MTBE)

Methyl Tertiary Butyl Ether, or MTBE, is a flammable additive that has made its way into groundwater by pollution. MTBE is now limited or banned in some states because of its effects on water quality.

Leaking gasoline storage containers can cause MTBE to leach into a public drinking water supply, typically in urban areas. Although the human health effects of MTBE have not yet been researched, animal studies have linked this additive to eye problems and skin irritation.

There is no national drinking water standard for MTBE, but many states have their own. In 1997, the EPA, issued a recommendation for 20 to 40 ppb or less MTBE in drinking water. Drinking water systems must monitor their MTBE levels and report back to the EPA.

mtbe groundwater pollution


Perchlorate is a chemical that is used in manufacturing fireworks, matches, signal flares, and vehicle airbag initiators. Perchlorate has been found naturally in dry, barren states in the southwest of the US. It dissolves easily and can make its way into food and drinking water sources.

Exposure to small amounts of perchlorate is considered to be fine, but higher quantities of perchlorate can affect the thyroid gland’s ability to transport iodide, resulting in an iodine deficiency. This affects the synthesis of thyroid hormones, which can in turn affect the body’s metabolic processes.

The maximum contaminant level for perchlorate is 8 mg/L.

🚰 How Are Chemicals in Tap Water Regulated?

Public water quality is regulated and monitored by the Safe Drinking Water Act and the Environmental Protection Agency.

These regulatory rules only apply to public water supplies. If you own a private well, it’s your responsibility to make sure your tap water is safe to drink.

Safe Drinking Water Act (SDWA)

The Safe Drinking Water Act, SDWA for short, came into place in 1974 in the U.S. All cities must adhere to this act, which sets a standard for tap water quality.

All public drinking water sources must meet the SDWA’s standards. This includes above-ground and underground water supplies.

The Safe Drinking Water Act aims to protect human health. This Act sets limitations on the man-made and naturally-occurring contaminants that are often found in tap water supplies.

Environmental Protection Agency (EPA)

The Environmental Protection Agency (EPA) monitors public drinking water suppliers using real-time online water monitoring tools. The EPA uses the data from its findings to ensure that water treatment facilities are taking the correct measures to provide safe drinking water to their customers. Data can also be used to identify trends or emerging problems and characterize water sources.

The EPA has produced a set of Maximum Contaminant Levels (MCLs) that water suppliers must adhere to when treating drinking water. Cities must also perform scheduled tests on their water and provide customers with an annual water quality report.

The EPA’s MCLs apply to a variety of common drinking water impurities, including heavy metals, chemicals, microorganisms, and radionuclides.

The Environmental Working Group (EWG) also monitors water quality, and has more stringent standards than the EPA. However, public water systems aren’t obliged to follow the standards set by the Environmental Working Group.

🧪 How Can I Find Out What’s in My Tap Water?

Not all water supplies contain the same impurities. The quality of the groundwater in your local area, and the methods used to treat your water, will determine your water quality. For this reason, I recommend testing your water to find out exactly what it contains.

The easiest, most affordable method is to test your water at home with a DIY test kit.

These kits test for some of the most common tap water contaminants, like chlorine, hardness, and lead.

You will receive a pack of strips and a color chart. When you dip a strip in a sample of your water, it will change color. You can then compare the color of the strip to the color chart to work out what your water contains.

DIY test kit

Laboratory testing is better than using DIY test kits if you want the most accurate results. However, laboratory tests are more expensive.

I’ve produced a step-by-step guide on how to test your water for impurities, which you can find here.

water testing with tap score

❓ Tap Water Contaminants FAQs

What is the Worst Tap Water Contaminant?

All the contaminants on this list are considered toxic and can be dangerous to health. Lead is considered one of the worst tap water contaminants because it is accumulative, and because it’s so commonly found in public water supplies.

How Does the Environmental Protection Agency Set its Maximum Contaminant Levels?

The Environmental Protection Agency carries out extensive research before setting a maximum contaminant level for an impurity. The agency will determine the maximum quantity of a contaminant that won’t cause illness, disease, death, or other effects. After considering options for measuring and treating this impurity, the EPA will establish a maximum contaminant level, known as an MCL for short.

How Do I Know if My Water is Safe to Drink?

If you have access to a public water supply, you can ask for a water quality report from your supplier. public water systems should adhere to the EPA’s standards by law, but it can still be handy to know what your water contains in trace amounts. Alternatively, test your water, especially if you have a well water supply.

  • Jennifer Byrd
    Water Treatment Specialist

    For 20+ years, Jennifer has championed clean water. From navigating operations to leading sales, she's tackled diverse industry challenges. Now, at Redbird Water, she crafts personalized solutions for homes, businesses, and factories. A past Chamber President and industry advocate, Jennifer leverages her expertise in cutting-edge filtration and custom design to transform water concerns into crystal-clear solutions.

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