Contaminant Directory

PFOA is a per- and polyfluoroalkyl substance (PFAS) — a synthetic "forever chemical" that resists breaking down in water and the body.

PFOS is a PFAS "forever chemical" closely related to PFOA, historically used in stain- and water-repellent products and firefighting foam.

PFHxS is a shorter-chain PFAS "forever chemical" regulated under the EPA PFAS rule as part of a hazard index alongside other PFAS.

Lead is a toxic metal that usually enters drinking water from corrosion of lead service lines, solder, and household plumbing rather than from the source water.

TTHMs are disinfection by-products that form when chlorine reacts with natural organic matter in water. They are the trade-off of effective disinfection.

HAA5 is a group of five haloacetic acids — disinfection by-products that, like TTHMs, form when chlorine reacts with organic matter.

Hardness is dissolved calcium and magnesium picked up from rock and soil. It is an aesthetic and plumbing consideration, not a health-based contaminant.

Arsenic is a naturally occurring semi-metal that dissolves into groundwater from rock and soil, and can also enter water from mining and legacy agricultural chemicals.

Nitrate is a nitrogen compound that enters water mainly from fertilizer, animal waste, and septic systems — one of the most common contaminants in agricultural areas.

Chlorine is the disinfectant most utilities add to control bacteria and viruses as water travels through the pipes. A residual at your tap is a sign disinfection is working; some systems use chloramine for a longer-lasting residual.

Hexavalent chromium (chromium-6) is a form of chromium from industrial processes and some natural deposits — the contaminant made famous by the Erin Brockovich case.

Copper is a metal that usually enters drinking water from the corrosion of household copper pipes and brass fixtures rather than from the source water. Small amounts are an essential nutrient; the concern is elevated levels.

Fluoride occurs naturally in groundwater and is also added by many utilities at low levels to reduce tooth decay. It is regulated because very high natural levels can affect teeth and bones.

Nitrite is a nitrogen compound closely related to nitrate, formed as nitrate is converted in the environment or in treatment. It shares nitrate’s sources but is regulated at a lower level.

Barium is a metal that enters drinking water mostly through the natural erosion of mineral deposits, and sometimes from industrial discharge or oil-and-gas activity.

Selenium is a trace element that is an essential nutrient in tiny amounts but is regulated in drinking water because higher levels from natural deposits or runoff can be harmful.

Cadmium is a toxic metal that can enter water from the corrosion of galvanized pipes and from industrial discharge, mining, and runoff.

Inorganic mercury is a toxic metal that reaches water from natural deposits, industrial discharge, and runoff. The drinking-water rule addresses inorganic mercury, distinct from the methylmercury that builds up in fish.

Antimony is a metal that can enter drinking water from natural deposits and from discharge related to petroleum refineries, fire retardants, ceramics, and electronics.

Uranium is a naturally occurring radioactive metal that dissolves into groundwater from uranium-bearing rock. It poses both a chemical (kidney) risk and a radiological one.

Radium is a naturally occurring radioactive element that dissolves into groundwater from rock and soil. It is regulated as the combined activity of radium-226 and radium-228.

Gross alpha is a combined measure of alpha-particle radioactivity in water — a screening figure for naturally occurring radionuclides such as radium and polonium (excluding radon and uranium).

Benzene is a volatile organic compound (VOC) found in gasoline and industrial solvents. It can reach groundwater from fuel leaks, industrial discharge, and landfills.

Trichloroethylene (TCE) is a volatile organic compound used as an industrial degreaser and solvent. It is a common groundwater contaminant near industrial and defense sites.

Tetrachloroethylene (PCE, "perc") is a volatile organic compound used in dry cleaning and metal degreasing. It reaches groundwater from dry-cleaner sites and industrial discharge.

Vinyl chloride is a volatile organic compound used to make PVC plastic. In water it often appears as a breakdown product of other solvents like TCE and PCE, and can leach from old PVC piping.

GenX (HFPO-DA) is a newer PFAS "forever chemical" introduced as a replacement for PFOA. It is now federally regulated both on its own and as part of a PFAS hazard index.

PFNA is a longer-chain PFAS "forever chemical" regulated under the EPA PFAS rule both individually and as part of a combined hazard index with other PFAS.

Microplastics are plastic fragments smaller than 5 millimetres — down to microscopic nanoplastics — that shed from packaging, textiles, tyres and the breakdown of larger plastic waste. They are an emerging contaminant: increasingly detected in tap and bottled water, but not yet federally regulated in drinking water.