Disinfectant, Other Chemicals in Tap Water Linked with Cancer

Previous scientific tests have revealed that public tap water may contain one or more contaminants that have been linked with serious health problems in humans.  Now researchers have done the math to estimate the risk of drinking contaminated tap water. Depending on the source where your community’s water comes from, your tap water may contain nitrates and trihalomethanes (the latter results from disinfectant chemicals reacting with water).  These chemicals are associated with an increased risk of rectal, colon, and bladder cancers.  Other problematic chemicals that have been found in tap water include arsenic and radioactive contaminants.  The types and levels of contaminants in tap water depend on the source of where your water comes from.

What is the risk from chemical compounds contaminating your tap water?

Exposure to multiple contaminants over time can have a cumulative effect on your health. The more contaminants we consume through water — and the longer we consume them — the greater our chance of getting sick from them.

The watchdog Environmental Working Group (EWG) set out to quantify this risk among tap water drinkers in the US. The researchers looked at 22 cancer-causing chemicals that were found in US drinking water from 2010 to 2017. Based on this data, they determined that water pollutants could lead to more than 100,000 cases of cancer among people who consume them for life.

Put another way, researchers predicted that four out of every 10,000 people who drink contaminated water for life could develop cancer as a result. (source)

Other highlights

-The EWG study focused on three types of pollutants: arsenic, radioactive contaminants, and disinfection byproducts.

-Researchers looked at data for the approximately 279 million people served by public water systems (about 86% of the US population).  Public water systems that do not track data were excluded from the study, as were people whose drinking water comes from private and community wells.

-The study identified arsenic as a contaminant that could lead to 45,000 cases of cancer.

-Disinfection byproducts* accounted for roughly 45,000 of the cancer cases predicted.

-Radioactive contaminants like radium and uranium, meanwhile, accounted for about 4,500 cases.

-The rest of the cases were associated with chemicals present in much smaller amounts, like benzene and hexavalent chromium.

*Disinfection byproducts are more prevalent in public water systems using surface-water, which include lakes and streams, because those systems are legally required to add a disinfectant like chlorine to the water supply.

The types and levels of contaminants in tap water depend on the source of where your water comes from.

-Small groundwater systems have the highest risk of contamination. That’s because they’re often located in areas that lack the funding and infrastructure to get rid of pollutants.

-Most public water systems in the US depend on surface water.

For those systems, contamination risks rise during times of drought, since there’s less water to dilute contaminants, which leads chemicals to concentrate in surface water. When surface water is scarce, communities are also forced to start pumping groundwater. (source)


Experts recommend the best way to reduce your risk of negative health effects from contaminated water is (1) to find out where your water comes from, and then (2) purchase a filter that’s designed to weed out contaminants in your local system.

Should you switch to bottled water?

The short answer is: No.  Switching to bottled water is not seen as necessary unless there has been serious water contamination such in the cases of Flint, Michigan and Newark, New Jersey.  A primary reason is because a quarter or more of bottled water is simply tap water that’s been bottled. Recent tests from the Center for Environmental Health found “high levels” of arsenic in bottled water brands owned by Whole Foods and Keurig Dr Pepper.

The takeaway: Contaminant-specific filters are the best solution for assuring that you and your family have safe, clean water coming from your taps.