EWG's Tap Water Database

Science Lab

EWG Reviewed Contaminants

Click on the contaminant name for more information.

ContaminantDescriptionNumber of States
detected / tested
1,4-Dioxane1,4-Dioxane is a solvent classified by the EPA as a likely human carcinogen. It contaminates groundwater in many states due to industrial wastewater discharges, plastic manufacturing runoff and landfill runoff. 45 / 50
ArsenicArsenic is a potent carcinogen and common contaminant in drinking water. Arsenic causes thousands of cases of cancer each year in the U.S. 50 / 50
AtrazineAtrazine is a herbicide commonly detected in drinking water that comes from cornfield and other agricultural runoff. It is a hormone disrupter that harms the male and female reproductive systems of people and wildlife. 38 / 49
Carcinogenic VOCsMany Volatile Organic Compounds (VOCs) are solvents that increase the risk of cancer, and harm the nervous system, fetal growth and child development. EWG's list includes the most potent cancer-causing VOCs found in drinking water.49 / 50
Chromium-6Chromium (hexavalent) is a carcinogen that commonly contaminates American drinking water. Chromium (hexavalent) in drinking water may be due to industrial pollution or natural occurrences in mineral deposits and groundwater. 50 / 50
CopperCopper enters tap water from copper plumbing pipes. High concentrations of copper in drinking water can be harmful for infants and people with Wilson's disease, a rare genetic disorder. 50 / 50
Disinfection byproductsDisinfection byproducts are cancer-causing contaminants that form during water treatment with chlorine and other disinfectants. Disinfection byproducts may also increase the risk of problems during pregnancy, and may harm fetal growth and development.50 / 50
LeadLead contaminates drinking water when it leaches from pipes and plumbing fixtures. Lead exposure during childhood permanently harms learning ability and behavior.50 / 50
ManganeseManganese is a naturally occurring element that is common in food and drinking water. Excessive manganese exposures may impair children's attention, memory and intellectual capacity. 50 / 50
NitrateNitrate, a fertilizer chemical, frequently contaminates drinking water due to agricultural and urban runoff, and discharges from municipal wastewater treatment plants and septic tanks. Excessive nitrate in water can cause oxygen deprivation in infants and increase the risk of cancer. 50 / 50
NitrosaminesNitrosamines are DNA-damaging, cancer-causing disinfection byproducts that form during water treatment with certain disinfectants such as chloramine.4 / 5
PerchloratePerchlorate, a component of rocket fuel, occurs both naturally and as a synthetic chemical. Ingested perchlorate interferes with thyroid function. Exposure to perchlorate during pregnancy and childhood can impair cognitive development.7 / 13
Perfluorinated chemicalsPerfluorinated chemicals are a group of synthetic compounds used in hundreds of products from nonstick pans to stain-repellent clothing, wire coatings and firefighting foam. These chemicals have been linked to endocrine disruption, accelerated puberty, liver and immune system damage, thyroid changes, and cancer risk.33 / 50
Radiological contaminantsRadiological contaminants leach into water from certain minerals and from mining. Drinking water contamination with radioactive substances increases the risk of cancer and may harm fetal development.50 / 50