Drinking Water Contaminants
EPA-regulated contaminants tracked across all U.S. water systems. Click any contaminant to see national data, health effects, and affected systems.
Heavy Metals
LeadDevelopmental delays in children, kidney problems, high blood pressure. No safe level of lead exposure for children.CopperShort-term: gastrointestinal distress. Long-term: liver or kidney damage. People with Wilson's disease are more sensitive.BariumIncrease in blood pressure at levels above the MCL. Long-term exposure can affect the cardiovascular system and kidneys.CadmiumKidney damage with long-term exposure. Classified as a probable human carcinogen. Bone disease (itai-itai) at very high doses.Chromium (total)Allergic dermatitis. Chromium-6 (hexavalent) is a known carcinogen linked to lung cancer and gastrointestinal tumors.Mercury (inorganic)Kidney damage. Neurological effects including tremors, memory loss, and mood changes with chronic exposure.ThalliumHair loss; changes in blood; kidney, intestine, or liver problems.BerylliumIntestinal lesions with long-term exposure. Beryllium is classified as a human carcinogen.
Metalloids
ArsenicIncreased risk of cancer (skin, bladder, lung). Thickening and discoloration of skin; numbness; circulatory problems.SeleniumHair or fingernail loss; numbness in fingers or toes; circulatory problems at levels above MCL.AntimonyIncrease in blood cholesterol; decrease in blood sugar with long-term exposure.
Inorganic Chemicals
NitrateInfants below 6 months can develop methemoglobinemia ('blue baby syndrome'). May also affect adults with certain conditions.FluorideDental fluorosis (cosmetic) at 2 mg/L. Skeletal fluorosis (bone damage) at 4 mg/L. Below 0.7 mg/L used for dental health.NitriteInfants below 6 months can develop methemoglobinemia ('blue baby syndrome'). Combined nitrate+nitrite limit is 10 mg/L.CyanideNerve damage or thyroid problems with long-term exposure. Disrupts cellular oxygen use.
Emerging Contaminants
PFAS (Per- and Polyfluoroalkyl Substances)Increased risk of certain cancers, immune system effects, thyroid hormone disruption, high cholesterol, reproductive effects.PerchlorateDisrupts thyroid hormone production; may affect metabolism, growth, and development. Particularly concerning for pregnant women and infants.
disinfectant
Disinfection Byproducts
microbial
Total Coliform BacteriaNot harmful themselves but indicate possible presence of harmful pathogens. E. coli indicates recent fecal contamination.CryptosporidiumCryptosporidiosis: watery diarrhea, stomach cramps, nausea. Life-threatening in immunocompromised individuals (HIV/AIDS, transplant patients).Giardia lambliaGiardiasis: diarrhea, gas, greasy stools, stomach cramps. Symptoms may last 2-6 weeks. Can cause chronic digestive issues.LegionellaLegionnaires' disease: severe pneumonia with fever, cough, and shortness of breath. Pontiac fever: milder flu-like illness.
Radionuclides
Radium-226 and Radium-228 (combined)Increased risk of cancer with long-term exposure. Bone cancer is of particular concern due to radium's affinity for bone tissue.UraniumKidney toxicity (chemical) and increased cancer risk (radiological). Primarily damages the kidneys with long-term exposure.RadonIncreased risk of lung cancer (from inhaling radon released from tap water). Stomach cancer risk from ingestion.