What's in your water. And what it does to you.
Deep-dive guides on the 103 EPA-regulated contaminants in US drinking water. Click any organ on the body to filter by health impact. Tap a contaminant to dive in.
Your AquaOx filters 300+ contaminants in total. These 103 are the ones the EPA actively monitors and the ones customers ask about most.
103 contaminants
Industrial chemicals
Acrylamide
A residual monomer from polyacrylamide flocculants used in water and wastewater treatment. IARC Group 2A probable human carcinogen and a known neurotoxin. EPA regulates by Treatment Technique, not by MCL.
Herbicides
Alachlor
A widely-used corn and soybean herbicide that runs off agricultural fields into groundwater. EPA-regulated, classified as a probable human carcinogen.
Aesthetic / cosmetic
Aluminum
EPA secondary standard range 0.05 to 0.2 mg/L (cosmetic, not enforceable) for discoloration and post-treatment turbidity. A debated link to long-term neurodegenerative disease has been studied for decades and remains unresolved.
Heavy metals
Antimony
A heavy metal used in flame retardants, solder, and PET-plastic manufacturing. Leaches into water from industrial discharge and from heated plastic containers. EPA MCL is 0.006 mg/L.
Heavy metals
Arsenic
A naturally occurring heavy metal classified by the EPA and IARC as a known human carcinogen. Contaminates groundwater across large parts of the United States, especially in the West and the Midwest.
Industrial chemicals
Asbestos
A Group 1 carcinogen most commonly entering tap water from deteriorating asbestos-cement pipes installed mid-century. EPA MCL is 7 million fibers per liter for fibers longer than 10 micrometers.
Herbicides
Atrazine
The second-most-used herbicide in the United States and one of the most frequently detected pesticides in drinking water. Heavily applied to corn, sorghum, and sugarcane.
Heavy metals
Barium
A heavy metal found naturally in groundwater across much of the US and discharged from drilling and metal-refining operations. EPA MCL is 2 mg/L, relatively high among regulated metals because barium is less acutely toxic at typical doses.
VOCs / solvents
Benz(a)anthracene
A polycyclic aromatic hydrocarbon (PAH) produced by combustion. Found in water contaminated by coal-tar runoff, asphalt sealants, and creosote.
VOCs / solvents
Benzene
A gasoline-derived industrial solvent and IARC Group 1 known human carcinogen. The most-feared VOC in groundwater, linked to leukemia at chronic exposure.
VOCs / solvents
Benzo(a)pyrene
A polycyclic aromatic hydrocarbon (PAH) and IARC Group 1 known human carcinogen. The EPA's marker compound for PAH contamination in drinking water.
Heavy metals
Beryllium
A lightweight industrial metal used in aerospace, defense, and electronics. Contaminates water near coal-fired power plants, metal refineries, and historic manufacturing sites.
Disinfection byproducts
Bromate
Forms when ozone disinfection meets bromide in source water. Classified as a probable human carcinogen and tightly regulated at 10 parts per billion.
Disinfection byproducts
Bromodichloromethane
A trihalomethane formed when chlorine reacts with bromide-containing source water. EPA-regulated, classified as a probable human carcinogen.
Disinfection byproducts
Bromoform
The fully-brominated trihalomethane. Forms in chlorinated water that also contains naturally-occurring bromide, more common in coastal and saline source waters.
Heavy metals
Cadmium
A Group 1 carcinogen and potent kidney toxin that leaches from galvanized pipe corrosion, industrial waste, and old lead-solder impurities. EPA MCL is 0.005 mg/L.
Insecticides
Carbofuran
A highly toxic carbamate insecticide that inhibits the cholinesterase enzyme essential for nervous-system function. EPA cancelled all food-crop uses in 2009, but legacy contamination persists in groundwater.
VOCs / solvents
Carbon Tetrachloride
A formerly common solvent and dry cleaning fluid banned from consumer products. Now a legacy groundwater contaminant near old industrial sites and refrigerant manufacturers.
Treatment additives
Chloramine
Chlorine combined with ammonia. Used by roughly one in five US utilities because it lasts longer in distribution pipes than free chlorine.
Insecticides
Chlordane
A persistent organochlorine insecticide used heavily on US homes and crops from 1948 until its ban in 1988. Still detected in soil and groundwater decades later.
Treatment additives
Chlorine
The disinfectant most US utilities add to kill pathogens. Effective at its job, but it doesn't stop reacting once it leaves the treatment plant.
Treatment additives
Chlorine Dioxide
A reactive yellow-green gas some utilities use as a primary or pre-disinfectant. Effective against tough pathogens, but tightly regulated because of its byproduct chlorite.
Disinfection byproducts
Chlorite
The main byproduct of chlorine dioxide disinfection. Regulated by the EPA because of effects on red blood cells and developing infants.
VOCs / solvents
Chlorobenzene
A chemical-industry solvent and intermediate used to make pesticides, dyes, and rubber chemicals. Contaminates groundwater through industrial discharge.
Disinfection byproducts
Chloroform
The single most common disinfection byproduct in chlorinated tap water. Forms when chlorine reacts with naturally-occurring organic matter.
Heavy metals
Chromium
A heavy metal that exists in two main forms: trivalent chromium (a trace nutrient) and hexavalent chromium-6 (a known carcinogen). The hexavalent form contaminates municipal supplies in dozens of US states.
Heavy metals
Chromium-6
The toxic, carcinogenic form of chromium made famous by Erin Brockovich and the Hinkley, California groundwater case. EPA has no separate federal limit yet; California regulates it at 10 µg/L.
Heavy metals
Copper
An essential nutrient in trace amounts that becomes toxic at the levels that leach from copper plumbing into corrosive water. EPA action level is 1.3 mg/L.
Microbiological
Cryptosporidium
A chlorine-resistant parasite that causes severe diarrheal illness. The 1993 Milwaukee outbreak sickened 400,000 people and killed at least 50.
Industrial chemicals
Cyanide
A fast-acting industrial toxin from metal plating, mining, and chemical manufacturing waste. Blocks cellular oxygen use at acute doses. EPA MCL is 0.2 mg/L as free cyanide.
Herbicides
Dalapon
A chlorinated herbicide used to control unwanted grasses along roadsides, in orchards, and around irrigation ditches. EPA-regulated due to kidney effects at chronic exposure.
Industrial chemicals
Di(2-ethylhexyl) adipate
A plasticizer used in food wrap, plastic tubing, and PVC products. DEHA leaches from plastics into water and food, particularly when materials are warm or in contact with fatty substances.
Industrial chemicals
Di(2-ethylhexyl) phthalate
The most widely used plasticizer in flexible PVC. DEHP leaches from plastic pipes and consumer products into drinking water and is a documented endocrine disruptor.
Disinfection byproducts
Dibromochloromethane
A mixed bromine-chlorine trihalomethane. Forms in chlorinated water with moderate bromide content, and is regulated together with chloroform and the other THMs.
Disinfection byproducts
Dichloroacetic Acid
One of the five haloacetic acids regulated as a group in chlorinated water. Forms in the same disinfection reaction that produces THMs.
VOCs / solvents
o-Dichlorobenzene
An industrial solvent and chemical intermediate (1,2-dichlorobenzene). Used in pesticide and dye manufacture and as a degreaser.
VOCs / solvents
P-dichlorobenzene 1,4-Dichlorobenzene (p-DCB)
The active ingredient in mothballs and toilet bowl deodorizers. A household-source VOC that also contaminates groundwater near chemical and waste sites.
VOCs / solvents
1,1-Dichloroethene
An industrial chemical and breakdown product of trichloroethane in groundwater. Used to make food wrap and other plastics; regulated by the EPA at 7 ppb.
VOCs / solvents
1,2-Dichloroethylene
The trans isomer of 1,2-DCE, primarily a breakdown product of trichloroethylene and tetrachloroethylene in groundwater. Indicates a larger chlorinated solvent plume nearby.
VOCs / solvents
cis-1,2-Dichloroethylene
An industrial solvent and breakdown product of trichloroethylene (TCE). Found in groundwater near industrial sites, dry cleaners, and Superfund areas.
Herbicides
2,4-Dichlorophenoxyacetic Acid
One of the most widely used herbicides in the world, applied to lawns, wheat, corn, and pasture to kill broadleaf weeds. Detected in surface and groundwater across North America.
VOCs / solvents
1,2-Dichloropropane
A soil fumigant and industrial solvent classified as a probable human carcinogen. A major groundwater contaminant in Hawaii and California's Central Valley from decades of agricultural use.
Herbicides
Dinoseb
A nitrophenol herbicide banned by the EPA in 1986 due to severe reproductive and developmental toxicity. Still detected in groundwater in regions where it was heavily applied.
Industrial chemicals
Dioxin
Among the most toxic synthetic chemicals ever measured. Forms during combustion and industrial chemistry; accumulates in fat and persists in the body for decades.
Herbicides
Diquat
A non-selective contact herbicide used to control aquatic weeds, desiccate crops before harvest, and clear vegetation. EPA-regulated due to kidney and liver toxicity.
Microbiological
E. coli & Total Coliforms
Escherichia coli is the EPA's red-flag indicator of fecal contamination in drinking water. Any detection is a violation and triggers a boil-water advisory.
Herbicides
Endothall
An aquatic herbicide applied directly to lakes, ponds, and irrigation canals to control submerged and floating weeds. Also used as a pre-harvest desiccant on cotton and potatoes.
Insecticides
Endrin
A highly toxic organochlorine insecticide banned in the United States in 1986. Persistent in soil and sediment, still detected at low levels in groundwater near former use areas.
Industrial chemicals
Epichlorohydrin
A residual monomer from epichlorohydrin-based polymers used as coagulants in water treatment and in epoxy resins lining pipes and tanks. IARC Group 2A probable human carcinogen. EPA regulates by Treatment Technique.
VOCs / solvents
Ethylbenzene
A petroleum-derived solvent and key BTEX compound. Found in groundwater near gas stations, refineries, and styrene production sites.
VOCs / solvents
Ethylene Dibromide
A legacy gasoline additive and grain fumigant. A known reproductive toxicant and probable carcinogen regulated by the EPA at one of the lowest drinking-water limits, 0.05 ppb.
Well water
Fluoride
Added to most US municipal water for dental-health benefits, and naturally present in many well-water sources. Whole-house carbon reduces fluoride only partially; reverse osmosis removes it fully.
Microbiological
Giardia lamblia
A waterborne parasite that causes the persistent diarrheal illness known as giardiasis or 'beaver fever.' The most commonly diagnosed intestinal parasite in the United States.
Herbicides
Glyphosate
The active ingredient in Roundup and the most widely used herbicide on the planet. IARC classifies it as probably carcinogenic; EPA disagrees. Federally regulated at 0.7 mg/L in US drinking water.
Radionuclides
Gross Alpha Particle Activity
A composite measure of alpha-emitting radioactivity in water, used as the EPA's first-line screen for radionuclide contamination. Excludes radon and uranium, which are tested separately.
Disinfection byproducts
Haloacetic Acids (HAAS)
A regulated family of five disinfection byproducts that form alongside THMs when chlorine reacts with organic matter. The EPA caps the combined total at 60 ppb.
Insecticides
Heptachlor
A persistent organochlorine insecticide used heavily on corn, citrus, and around homes for termite control until banned in 1988. Breaks down into the more persistent heptachlor epoxide.
Insecticides
Heptachlor Epoxide
The breakdown product of the banned insecticide heptachlor. More persistent than the parent compound and the dominant residue found in soil, groundwater, and human tissue.
VOCs / solvents
Hexachlorobenzene
A banned fungicide and persistent organic pollutant. Bioaccumulates in fatty tissue and remains in the environment for decades after release.
VOCs / solvents
Hexachlorocyclopentadiene (HCCPD)
A chemical intermediate used to make organochlorine pesticides and flame retardants. Found in groundwater near former pesticide manufacturers and chemical waste sites.
Well water
Hydrogen Sulfide
The rotten-egg smell in well water. Produced by sulfur-reducing bacteria and geological sulfur deposits. Not acutely toxic at typical home levels but corrosive to plumbing and unpleasant.
Well water
Iron
The most common well-water nuisance. Iron dissolves out of soil and rock into groundwater, then oxidizes on contact with air to leave orange and brown stains on fixtures, laundry, and skin.
Heavy metals
Lead
A potent neurotoxin with no safe exposure level for children. Leaches into tap water from corroding lead service lines, lead solder, and brass fixtures, especially in homes built before 1986.
Microbiological
Legionella
The bacterium behind Legionnaires' disease, a severe form of pneumonia contracted by inhaling aerosolized droplets from contaminated showers, faucets, and cooling systems.
Insecticides
Lindane
A persistent organochlorine insecticide used for decades on crops, livestock, and as a treatment for lice and scabies. Banned for agricultural use in the United States in 2007 and globally restricted under the Stockholm Convention.
Aesthetic / cosmetic
Manganese
EPA secondary standard 0.05 mg/L (cosmetic, not enforceable) for the black and brown staining manganese leaves on fixtures and laundry. A separate health-based advisory of 0.3 mg/L exists because high manganese is associated with neurodevelopmental effects in children.
Heavy metals
Mercury
A heavy metal neurotoxin that enters water from coal combustion, mining, and industrial discharge. Methylmercury, the organic form, is one of the most toxic compounds in the environment.
Insecticides
Methoxychlor
An organochlorine insecticide once marketed as a safer substitute for DDT. Used on crops, livestock, and home gardens until the EPA cancelled all uses in 2003 over endocrine and reproductive concerns.
Emerging concerns
Microplastics
Plastic fragments smaller than 5 mm that are now detected in nearly every drinking water supply tested worldwide. Federally unregulated; California became the first US state to set a standard.
VOCs / solvents
MTBE (Methyl Tertiary-Butyl Ether)
A gasoline oxygenate used heavily from 1979 through the mid-2000s that contaminated thousands of US groundwater supplies through leaking underground storage tanks. No federal MCL; many states regulate.
Heavy metals
Nickel
A common industrial metal used in stainless steel, plating, and batteries. Triggers contact dermatitis in sensitized people and irritates airways through inhaled shower vapor.
Well water
Nitrate
The most common chemical contaminant in US private wells. Causes potentially fatal methemoglobinemia (blue baby syndrome) in infants. Activated carbon does not remove nitrate; reverse osmosis does.
Insecticides
Oxamyl
A carbamate insecticide sold as Vydate, used on potatoes, citrus, and field crops. EPA-regulated due to acute neurological toxicity.
Industrial chemicals
Pentachlorophenol
A chlorinated wood preservative phased out for residential use in 1987 but still contaminating soil and groundwater at industrial sites. EPA-classified as a likely human carcinogen.
Emerging concerns
PFAS (Forever Chemicals)
A family of synthetic fluorinated compounds (PFOA, PFOS, PFNA, PFHxS, GenX) that resist degradation, accumulate in the body for years, and are now federally regulated at parts-per-trillion levels.
Emerging concerns
Pharmaceuticals
Trace residues of human and veterinary medications (antibiotics, hormones, antidepressants, painkillers) that pass through wastewater treatment and into source water for downstream utilities.
Herbicides
Picloram
A broadleaf herbicide sold as Tordon, used on pastures, rangeland, and rights-of-way. Highly persistent and mobile in groundwater.
Industrial chemicals
Polychlorinated Biphenyls (PCBs)
Industrial coolants and insulating fluids banned in 1979. PCBs persist in the environment for decades, bioaccumulate in fat tissue, and concentrate up the food chain.
Radionuclides
Radium (Ra-226 + Ra-228)
A naturally occurring radioactive element that behaves like calcium in the body, depositing in bone where it can irradiate marrow for decades.
Radionuclides
Radon
A radioactive noble gas produced by uranium decay. The second-leading cause of lung cancer in the US, with shower-water aerosolization a documented exposure route.
Insecticides
S-chloropropane (DBCP)
Dibromochloropropane (DBCP), a banned soil fumigant that sterilized chemical-plant workers in the 1970s. Persistent groundwater contamination across California, Hawaii, and Arizona.
Heavy metals
Selenium
An essential trace nutrient that becomes neurotoxic and dermatologic above the EPA limit of 0.05 mg/L. High-selenium groundwater is common in parts of the western United States.
Herbicides
Silvex 2,4,5-TP
A chlorinated herbicide banned in 1985 due to dioxin contamination during manufacture. Legacy soil and groundwater contamination persists at former application sites.
Herbicides
Simazine
A triazine herbicide closely related to atrazine, used on corn, sugarcane, and orchards. Frequently detected in groundwater across the corn belt.
VOCs / solvents
Styrene
A precursor to polystyrene plastic and synthetic rubber. Contaminates groundwater through industrial discharge and landfill leaching.
Aesthetic / cosmetic
Sulfate
EPA secondary standard 250 mg/L (cosmetic, not enforceable) for the bitter taste sulfate gives water. At higher levels it acts as a laxative, particularly in infants and visitors not adapted to the local supply.
VOCs / solvents
Tetrachloroethene
The classic dry cleaning solvent, also called perchloroethylene or perc. One of the most common groundwater contaminants in the United States and a probable human carcinogen.
Heavy metals
Thallium
One of the most toxic heavy metals on the periodic table, historically used in rat poison and infamous as a murder weapon. EPA MCL of 0.002 mg/L is among the lowest of any regulated inorganic.
VOCs / solvents
Toluene
A common gasoline-derived solvent in the BTEX family. Contaminates groundwater near gas stations, refineries, and industrial sites.
Aesthetic / cosmetic
Total Dissolved Solids (TDS)
EPA secondary standard 500 mg/L (cosmetic, not enforceable). TDS is the sum of every dissolved mineral in your water: calcium, magnesium, sodium, sulfate, bicarbonate, and more. High TDS affects taste and accelerates scale buildup but is not a direct health concern.
Insecticides
Toxaphene
A chlorinated insecticide once heavily used on cotton, banned in 1990 but persistent in soil, sediment, and fish for decades.
Disinfection byproducts
Trichloroacetic Acid
One of the five haloacetic acids regulated as a group in chlorinated water. Typically the most abundant HAA in low-bromide municipal supplies.
VOCs / solvents
1,2,4-Trichlorobenzene
An industrial solvent and dye carrier with limited modern use. Found in groundwater near chemical plants, textile mills, and former waste disposal sites.
VOCs / solvents
1,1,1-Trichloroethane
An industrial degreasing solvent phased out under the Montreal Protocol for depleting the ozone layer. Still found in groundwater near former industrial sites and old waste disposal areas.
VOCs / solvents
1,1,2-Trichloroethane
A chemical intermediate used to make vinylidene chloride and other industrial compounds. Classified by the EPA as a probable human carcinogen and regulated at 5 ppb in drinking water.
VOCs / solvents
Trichloroethylene (TCE)
An industrial metal degreasing solvent and one of the most common groundwater contaminants in the United States. Classified by the EPA as a known human carcinogen causing kidney cancer.
VOCs / solvents
1,2,3 Trichloropropane (TCP)
A chlorinated solvent and pesticide impurity. A known human carcinogen with no federal MCL, but California regulates it at an extremely strict 5 parts per trillion.
Disinfection byproducts
Trihalomethane (TTHM)
The EPA's regulatory grouping for the four most common chlorinated/brominated THMs. Capped at 80 ppb combined in every US municipal supply.
Radionuclides
Uranium
A naturally occurring radioactive metal that leaches into groundwater from uranium-bearing rock. Both chemically toxic to the kidneys and radiologically active in bone.
VOCs / solvents
Vinyl Chloride
An IARC Group 1 known human carcinogen tied to liver angiosarcoma. Enters drinking water from old PVC pipe degradation, landfill leachate, and as the final breakdown product of TCE and PCE plumes.
Aesthetic / cosmetic
Water Hardness
Hardness is the calcium and magnesium dissolved in your water, measured as calcium carbonate equivalent. The EPA does not regulate it, but it is the single most common reason people call us: scale buildup, soap scum, dry skin, and shortened appliance life all trace back to it.
VOCs / solvents
Xylenes
Three isomers of dimethylbenzene found in gasoline. Part of the BTEX family that contaminates groundwater from fuel leaks and industrial discharge.
Aesthetic / cosmetic
Zinc
EPA secondary standard 5 mg/L (cosmetic, not enforceable). Zinc gives water a metallic, slightly astringent taste and a milky appearance at higher levels. The most common source is corrosion of old galvanized steel plumbing.
See your water's report card
Most US households can pull a free EPA-mandated annual Consumer Confidence Report from their utility. Or test your own water with an independent lab.