Source:  Source Water Contaminants classified by USGS

Contaminant Sources to groundwater Potential health and other effects
Aluminum Occurs naturally in some rocks and drainage from mines. Can precipitate out of water after treatment, causing increased turbidity or discolored water.
Antimony Enters environment from natural weathering, industrial production, municipal waste disposal, and manufacturing of flame retardants, ceramics, glass, batteries, fireworks, and explosives. Decreases longevity, alters blood levels of glucose and cholesterol in laboratory animals exposed at high levels over their lifetime.
Arsenic Enters environment from natural processes, industrial activities, pesticides, and industrial waste, smelting of copper, lead, and zinc ore. Causes acute and chronic toxicity, liver and kidney damage; decreases blood hemoglobin. A carcinogen.
Barium Occurs naturally in some limestones, sandstones, and soils in the eastern United States. Can cause a variety of cardiac, gastrointestinal, and neuromuscular effects. Associated with hypertension and cardiotoxicity in animals.
Beryllium Occurs naturally in soils, groundwater, and surface water. Often used in electrical industry equipment and components, nuclear power and space industry. Enters the environment from mining operations, processing plants, and improper waste disposal. Found in low concentrations in rocks, coal, and petroleum and enters the ground and Causes acute and chronic toxicity; can cause damage to lungs and bones. Possible carcinogen.
Cadmium Found in low concentrations in rocks, coal, and petroleum and enters the groundwater and surface water when dissolved by acidic waters. May enter the environment from industrial discharge, mining waste, metal plating, water pipes, batteries, paints and pigments, plastic stabilizers, and landfill leachate. Replaces zinc biochemically in the body and causes high blood pressure, liver and kidney damage, and anemia. Destroys testicular tissue and red blood cells. Toxic to aquatic biota.
Chloride May be associated with the presence of sodium in drinking water when present in high concentrations. Often from saltwater intrusion, mineral dissolution, industrial and domestic waste. Deteriorates plumbing, water heaters, and municipal water-works equipment at high levels.
Above secondary maximum contaminant level, taste becomes noticeable.
Chromium Enters environment from old mining operations runoff and leaching into groundwater, fossil-fuel combustion, cement-plant emissions, mineral leaching, and waste incineration. Used in metal plating and as a cooling-tower water additive. Chromium III is a nutritionally essential element. Chromium VI is much more toxic than Chromium III and causes liver and kidney damage, internal hemorrhaging, respiratory damage, dermatitis, and ulcers on the skin at high concentrations.
Copper Enters environment from metal plating, industrial and domestic waste, mining, and mineral leaching. Can cause stomach and intestinal distress, liver and kidney damage, anemia in high doses. Imparts an adverse taste and significant staining to clothes and fixtures. Essential trace element but toxic to plants and algae at moderate levels.
Cyanide Often used in electroplating, steel processing, plastics, synthetic fabrics, and fertilizer production; also from improper waste disposal. Poisoning is the result of damage to spleen, brain, and liver.
Dissolved solids Occur naturally but also enters environment from man-made sources such as landfill leachate, feedlots, or sewage. A measure of the dissolved “salts” or minerals in the water. May also include some dissolved organic compounds. May have an influence on the acceptability of water in general. May be indicative of the presence of excess concentrations of specific substances not included in the Safe Water Drinking Act, which would make water objectionable. High concentrations of dissolved solids shorten the life of hot water heaters.
Fluoride Occurs naturally or as an additive to municipal water supplies; widely used in industry. Decreases incidence of tooth decay but high levels can stain or mottle teeth. Causes crippling bone disorder (calcification of the bones and joints) at very high levels.
Hardness Result of metallic ions dissolved in the water; reported as concentration of calcium carbonate. Calcium carbonate is derived from dissolved limestone or discharges from operating or abandoned mines. Decreases the lather formation of soap and increases scale formation in hot-water heaters and low-pressure boilers at high levels.
Iron Occurs naturally as a mineral from sediment and rocks or from mining, industrial waste, and corroding metal. Imparts a bitter astringent taste to water and a brownish color to laundered clothing and plumbing fixtures.
Lead Enters environment from industry, mining, plumbing, gasoline, coal, and as a water additive. Affects red blood cell chemistry; delays normal physical and mental development in babies and young children. Causes slight deficits in attention span, hearing, and learning in children. Can cause slight increase in blood pressure in some adults. Probable carcinogen.
Manganese Occurs naturally as a mineral from sediment and rocks or from mining and industrial waste. Causes aesthetic and economic damage, and imparts brownish stains to laundry. Affects taste of water, and causes dark brown or black stains on plumbing fixtures. Relatively non-toxic to animals but toxic to plants at high levels.
Mercury Occurs as an inorganic salt and as organic mercury compounds. Enters the environment from industrial waste, mining, pesticides, coal, electrical equipment (batteries, lamps, switches), smelting, and fossil-fuel combustion. Causes acute and chronic toxicity. Targets the kidneys and can cause nervous system disorders.
Nickel Occurs naturally in soils, groundwater, and surface water. Often used in electroplating, stainless steel and alloy products, mining, and refining. Damages the heart and liver of laboratory animals exposed to large amounts over their lifetime.
Nitrate (as nitrogen) Occurs naturally in mineral deposits, soils, seawater, freshwater systems, the atmosphere, and biota. More stable form of combined nitrogen in oxygenated water. Found in the highest levels in groundwater under extensively developed areas. Enters the environment from fertilizer, feedlots, and sewage. Toxicity results from the body’s natural breakdown of nitrate to nitrite. Causes “bluebaby disease,” or methemoglobinemia, which threatens oxygen-carrying capacity of the blood.
Nitrite (combined nitrate/nitrite) Enters environment from fertilizer, sewage, and human or farm-animal waste. Toxicity results from the body’s natural breakdown of nitrate to nitrite. Causes “bluebaby disease,” or methemoglobinemia, which threatens oxygen-carrying capacity of the blood.
Selenium Enters environment from naturally occurring geologic sources, sulfur, and coal. Causes acute and chronic toxic effects in animals–“blind staggers” in cattle. Nutritionally essential element at low doses but toxic at high doses.
Silver Enters environment from ore mining and processing, product fabrication, and disposal. Often used in photography, electric and electronic equipment, sterling and electroplating, alloy, and solder. Because of great economic value of silver, recovery practices are typically used to minimize loss. Can cause argyria, a blue-gray coloration of the skin, mucous membranes, eyes, and organs in humans and animals with chronic exposure.
Sodium Derived geologically from leaching of surface and underground deposits of salt and decomposition of various minerals. Human activities contribute through de-icing and washing products. Can be a health risk factor for those individuals on a low-sodium diet.
Sulfate Elevated concentrations may result from saltwater intrusion, mineral dissolution, and domestic or industrial waste. Forms hard scales on boilers and heat exchangers; can change the taste of water, and has a laxative effect in high doses.
Thallium Enters environment from soils; used in electronics, pharmaceuticals manufacturing, glass, and alloys. Damages kidneys, liver, brain, and intestines in laboratory animals when given in high doses over their lifetime.
Zinc Found naturally in water, most frequently in areas where it is mined. Enters environment from industrial waste, metal plating, and plumbing, and is a major component of sludge. Aids in the healing of wounds. Causes no ill health effects except in very high doses. Imparts an undesirable taste to water. Toxic to plants at high levels.