| Contaminant | Health Effects | Sources |
| Total coliform | Not necessarily disease-causing themselves, coliforms can be indicators of organisms that can cause gastroenteric infections, dysentery, hepatitis, typhoid fever, cholera, and others. Also, coliforms interfere with disinfection. | Human and animal fecal matter |
| Turbidity | Interferes with disinfection | Erosion, runoff, discharges |
| Giardia lamblia | Giardiasis (stomach cramps, intestinal distress) | Human and animal fecal matter |
| Enteric viruses | Gastroenteritis (intestinal distress) | Human and animal fecal matter |
| Legionella | Legionnaires’ disease (pneumonia), Pontiac Fever | Water aerosols such as vegetable misters |
| Arsenic | Dermal and nervous system toxicity effects | Geological, pesticide residues, industrial wastes, smelter operations |
| Barium | Circulatory system effects | Geological, pesticide residues, industrial wastes, smelter operations |
| Cadmium | Kidney effects | Geological, mining, and smeltering |
| Chromium | Liver and kidney effects | Geological, mining, and smeltering |
| Fluoride | Skeletal damage | Geological, additive to drinking water, toothpaste, foods process with fluoridated water |
| Mercury | Central nervous system disorders, kidney effects | Used in manufacture of paint, paper, vinyl chloride and fungicides. Geological |
| Selenium | Gastrointestinal effects | Geological, mining |
| Endrin | Nervous system/kidney effects | Insecticide used on cotton, small grains, orchards (canceled) |
| Methoxychlor | Nervous system/kidney effects | Insecticide used on fruit trees, vegetables |
| Toxaphene | Cancer risk (potentially carcinogenic) | Insecticide used on cotton, corn, grains |
| 2,4,5–TP | Liver/kidney effects | Herbicide, canceled in 1984 |
| Benzene | Cancer (carcinogen) | Fuel (leaking tanks), solvent commonly used in manufacture of industrial chemicals, pharmaceuticals, pesticides, paints, and plastics |
| 1,2–dichloroethane | Cancer risk (potentially carcinogenic) | Used in manufacture of insecticides, gasoline |
| Trichloroethylene | Cancer risk (potentially carcinogenic) | Waste from disposal of dry cleaning materials, and manufacture of pesticides, paints, waxes and varnishes, paint stripper, metal degreaser |
| Para-dichlorobenzene | Cancer risk (potentially carcinogenic) | Used in insecticides, moth balls, air deodorizers |
| 1,1,1–trichloroethane | Nervous system effects | Used in manufacture of food wrappings, synthetic fibers |
| Gross alpha | Cancer (carcinogen) | Radioactive waste, uranium deposits |
| Radium 226 & 228 | Bone cancer (carcinogen) | Radioactive waste, geological |
| Gross beta | Cancer (carcinogen) | Radioactive waste, uranium deposits |