7 Common Contaminants Found in Drinking Water

Let us start by saying that generally, in the U.S. public water is well-regulated and is, for the most part, safe to drink. That’s not to say that there aren’t any impurities that make it into your water supply in trace amounts. “Drinking water supplies in the United States are among the safest in the world. However, even in the U.S., drinking water sources can become contaminated,” notes the Centers for Disease Control and Prevention (CDC).

In particular, people on well water in more rural areas could have a higher risk of health impacts from contaminants in their tap water, making regular testing important. That being said, here are seven substances found in municipal and well water that may warrant a water purifier at home if you’re concerned…

1. Human/Animal Fecal Matter

The Environmental Protection Agency (EPA) offers a table of regulated drinking water contaminants, adding the “National Primary Drinking Water Regulations (NPDWR) are legally enforceable primary standards and treatment techniques that apply to public water systems.”

That being said, contaminants including Cryptosporidium and Giardia lamblia (generally in private wells) from fecal matter can make their way into water supplies, causing gastrointestinal illnesses and cramps from long-term exposure, notes the EPA.


2. Legionella

The EPA notes that legionella bacteria are actually a naturally occurring contaminant in water, which can lead to Legionnaires’ disease (a type of serious lung infection). While it’s normally spread through tiny water droplets in the air, usually in buildings with larger plumbing systems, it can make it’s way into your body by aspiration of drinking water (when water “goes down the wrong pipe”, notes the CDC).

While this bacterium doesn’t often affect healthy people, there are certain groups that could be at more risk – including seniors, smokers, or those with a chronic lung condition or weakened immune system, adds the source.

legionella bacteria

3. Nitrate

This is most common in rural areas, typically in private water systems, and is the result of runoff from fertilizers and manure storage, according to a post from Cornell University. Heightened nitrate can cause Methemoglobinemia, a blood condition from the formation of an abnormal type of hemoglobin (that distributes oxygen in the body).  

While nitrate is often absorbed by plants or carried away in surface runoff, it can leach into groundwater, adds the source. This can elevate nitrogen in drinking water and make it unsafe to consume. Even septic systems used in rural areas can be a source of this problem, “because they remove only half of the nitrogen in wastewater, leaving the remaining half to percolate to groundwater,” explains the post.

well water

4. Chlorine

This is a chemical you probably only associate with pool water, but it is also used to kill bacterial impurities in drinking water supplies. However, while chlorine can reduce the risk from pathogens in the water, there’s some concern it could be adding other health risks.

The Water Research Center explains that some of the chlorine present in well water may not be dissolved (referred to as “free chlorine”). It also explains that Trihalomethanes (THMs) when organic materials combine with free chlorine, and those THMs “are linked to increases in some cancers.” However, it adds that the health risks from drinking untreated water are much higher than consuming THMs.


5. Arsenic

The Natural Resources Defense Council (NRDC) explains that in the year 2000, around 36-million Americans consumed drinking water containing arsenic at a concentration of 3-parts per billion or more. Mind you, this was some time ago, and the source acknowledges “arsenic levels across the country have declined as a result,” although people should still be vigilant.

The council said you should start by taking a closer look at the annual Consumer Confidence Report that is distributed by local water suppliers, as it shows any contaminants that could be posing a risk. Long-term exposure to arsenic in drinking water can cause cancer of the skin, lungs, kidney and bladder, notes various sources.

water treatment

6. Aluminum

The Water Quality Association explains that aluminum content in water is typically a result of leaching from rocks and soil. It is “extremely abundant” in the earth’s crust, and can exist in any water source, usually in small concentrations.

Although aluminum is regulated in public drinking water, Secondary Maximum Contaminant Level guidelines are used – which looks at changes in color and smell, notes the source. The EPA recommends levels of below 0.05-parts per million of aluminum in water, while the World Health Organization (WHO) aims for 0.2-ppm. Some sources say elevated aluminum can have adverse affects on the nervous system, but the association notes, “studies linking aluminum in drinking water to human health issues have been inconclusive”.


7. Lead

This is another contaminant on the EPA’s watch list, as lead content in drinking water has been linked to developmental delays in children, notes the source. It typically ends up in water supplies through corrosion of older plumbing systems or from natural deposits.

The EPA also agrees “that there is no known safe level of lead in a child’s blood,” and refers to the Comsumer Confidence Report to determine if there’s lead in your municipal supply. You should contact your local health department if you have concerns about your private water supply, adds the EPA. Better yet, have your water tested by a local lab – it’s a relatively inexpensive test that can give you the untainted truth about lead content in your water. If you have an older home with lead pipes, replace them or at least let the tap run for a time before filling your glass.

water test

Jeff Hayward

Jeff Hayward

Jeff has more than 15 years of experience writing professionally about health, travel and the arts among other subjects. He continuously looks to improve his own overall health through exercise, diet and mindfulness. He is also a proud stay-at-home dad that loves taking photographs both professionally and as a hobby.