Volatile organic compounds (VOCs) are a group of chemicals increasingly found in drinking water that can cause a range of health effects—including cancer.

VOCs are used everywhere from industry, agriculture, transportation, and in day-to-day household products. Unfortunately, once these chemicals contaminate local groundwater, they are difficult to remove. We’ll go over what VOCs are, where they’re found, how to detect VOCs, health risks, and what you can do to protect your water.

VOCs are carbon-containing compounds with properties that allow them to easily evaporate and move between the air, soil, surface water, and groundwater.

We encounter VOCs all the time in daily life as additives in gasoline, paints, varnishes, and cleaners. Many familiar chemical-related smells—like a freshly painted wall or an uncapped permanent marker—are actually scents caused by VOCs. They have several commercial and industrial uses including the manufacturing of automobiles, electronics, and plastics.

According to a 2006 U.S. Geological Survey study, 90 of 98 aquifers nationwide tested positive for at least one VOC.

The most frequent detections occurred in California, Nevada, Florida, as well as the New England and mid-Atlantic states.

VOCs easily dissolve and leach into groundwater, and most VOCs found in drinking water are caused by human activity.

Because VOCs spread easily and are long lasting, private wells located near industrial or commercial areas, gas stations, landfills, railroad tracks or farm fields can be at risk of VOC contamination. These chemicals can enter drinking water systems through leaks, accidental spills, and improper disposal.

The most commonly detected VOC groups include:

Many VOCs produce an odor in water, giving off a sweet, gasoline-like, or chemical smell. High concentrations may also result in an iridescent, oily sheen on the surface of your water. However, oftentimes, disinfection byproducts cause no changes to water’s smell, appearance, or taste at all.

Contacting your local utility or public health department is a good first step toward finding out which contaminants may be in your drinking water distribution system.

However, testing is the only way to know the actual concentration of VOCs in water.

It is always advisable to test your water after any major changes to its taste, smell, or appearance.

If your drinking water comes from a utility/city water supply, it is most likely treated with chlorine to kill any waterborne pathogens. When the chlorine reacts with naturally occurring organic matter in your pipes, various (and potentially carcinogenic) VOCs form as disinfection byproducts. It is strongly recommended that when testing city water a VOC panel is also included.

Testing well water for VOCs is recommended at least every 3 to 5 years, though consider more frequent testing if you live near a landfill, factory, gas station, fuel tank, or dry-cleaning operation. VOCs can also be found if your well is located near agricultural, mining, or industrial activity. Alternatively, if you have recently performed a shock chlorination on your well to remove bacteria, it is also suggested you test for VOCs to ensure any lingering chlorine or related compounds have dissipated to safe levels.

Whether you get your water from the city or if you have a private well, if your home has plastic pipes (PEX, PVC etc.), VOC testing is encouraged. Plastic plumbing, which has gained wide popularity in recent years, can leach a range of volatile organic compounds into your water.

VOCs are a wide variety of chemicals, and their health effects are varied and still the subject of study. However, several VOCs are linked to a range of short- and long-term health risks. Most adverse health effects happen when people are exposed to contaminated drinking water over a long period of time.

The Environmental Working Group lists 12 potentially carcinogenic VOCs (including 9 classified as such by the EPA):

Additionally, animal studies have found MTBE to cause kidney and liver tumors, as well as neurological effects in humans.

VOCs are also linked to other serious health risks like liver, kidneys and nerve damage (for example, toluene, ethylbenzene and xylene).

While the EPA has enforceable limits for 21 VOCs in tap water, these regulations have not been updated since 1992 and are not based on what's advisable for human health.