Water Contaminant Database: 100+ Contaminants (2026)
📅 Last Updated: July 16, 2026
Published January 2026 | Written by Filter Tested Editorial Team | Last updated: July 11, 2026 | Read our methodology
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Table of Contents
Quick Summary
This database catalogs over 100 contaminants found in drinking water supplies across the United States, organized into seven major categories. Each entry includes the contaminant's health effects, EPA Maximum Contaminant Level (MCL) where established, common sources, and the treatment technologies effective for its removal. Microorganisms include bacteria, viruses, and protozoan parasites that cause acute illness. Inorganic chemicals cover heavy metals, minerals, and radionuclides with chronic toxicity profiles. Organic chemicals encompass volatile organic compounds (VOCs), pesticides, herbicides, and industrial solvents. Disinfection byproducts (DBPs) form when chlorine reacts with organic matter. PFAS are a class of persistent synthetic chemicals receiving increasing regulatory attention. Physical and aesthetic parameters affect water appearance, taste, and corrosivity. Emerging contaminants include pharmaceuticals, microplastics, and other substances not yet regulated but detected in water supplies. Use the treatment technology reference at the end to identify which filtration systems address your specific water concerns.
How to Use This Database
This reference is organized by contaminant category. For each contaminant, the database provides: (1) the EPA Maximum Contaminant Level (MCL) or health advisory level in milligrams per liter (mg/L) or micrograms per liter (ug/L), (2) a summary of health effects, (3) common sources of contamination, and (4) effective treatment technologies. If you have concerns about specific contaminants in your water, start by reviewing your utility's annual Consumer Confidence Report (CCR), then cross-reference detected contaminants against this database to understand risks and identify appropriate treatment solutions.
Microorganisms (15 Contaminants)
Pathogenic microorganisms cause waterborne illness ranging from mild gastrointestinal distress to severe, life-threatening disease. They are the oldest and most immediate threat to drinking water safety. Treatment focuses on disinfection (UV, chlorine, ozone) and physical removal (filtration).
| Contaminant | Type | Health Effects | Treatment |
|---|---|---|---|
| E. coli (O157:H7) | Bacterium | Severe gastroenteritis, bloody diarrhea, hemolytic uremic syndrome (HUS), kidney failure. Infectious dose: 10-100 organisms. | UV disinfection, chlorination, ozonation, 0.1-micron filtration, RO |
| Legionella pneumophila | Bacterium | Legionnaires' disease (severe pneumonia), Pontiac fever. Grows in warm water systems (77-108-F). 10% mortality rate for Legionnaires'. | Heat pasteurization (>140-F), UV, copper-silver ionization, chlorination |
| Salmonella | Bacterium | Salmonellosis: diarrhea, fever, abdominal cramps. Can cause septicemia in immunocompromised individuals. | UV disinfection, chlorination, ozonation, microfiltration |
| Campylobacter jejuni | Bacterium | Campylobacteriosis: diarrhea, cramping, fever. Most common bacterial cause of diarrheal illness in the U.S. | UV, chlorination, microfiltration |
| Shigella | Bacterium | Shigellosis (bacillary dysentery): severe diarrhea with blood and mucus. Highly infectious. | UV, chlorination, ozonation |
| Vibrio cholerae | Bacterium | Cholera: profuse watery diarrhea, rapid dehydration, death within hours if untreated. Rare in developed countries. | Chlorination, UV, RO |
| Pseudomonas aeruginosa | Bacterium | Opportunistic infections: skin/eye infections, respiratory infections in immunocompromised individuals. | UV, chlorination, ozonation |
| Hepatitis A virus | Virus | Hepatitis A: liver inflammation, jaundice, fatigue, nausea. Can persist in water for months. | UV, chlorination (higher doses than bacteria), ozonation, RO |
| Norovirus | Virus | Acute gastroenteritis: vomiting, diarrhea, stomach cramps. Extremely infectious (10-100 particles). Leading cause of foodborne illness. | UV, chlorination, ozonation |
| Rotavirus | Virus | Severe diarrhea, vomiting, fever in infants and children. Vaccine-preventable but still prevalent in unvaccinated populations. | UV, chlorination, RO |
| Enteroviruses | Virus | Mild respiratory illness to meningitis, myocarditis, and polio (poliovirus). | UV, ozonation, chlorination |
| Adenovirus | Virus | Respiratory infections, conjunctivitis, gastroenteritis. Highly resistant to chlorination. | UV, ozonation |
| Giardia lamblia | Protozoan | Giardiasis: prolonged diarrhea, malabsorption, weight loss. Cysts resistant to chlorine at standard doses. EPA MCL: TT (99.9% removal) | UV, 1-micron absolute filtration, RO, chlorination (extended contact time) |
| Cryptosporidium parvum | Protozoan | Cryptosporidiosis: watery diarrhea, can be life-threatening in immunocompromised. Oocysts highly chlorine-resistant. EPA MCL: TT (99% removal) | UV, 1-micron absolute filtration, RO. Chlorination ineffective at standard doses. |
| Helminths (parasitic worms) | Helminth | Various intestinal and tissue infections depending on species. Rare in U.S. municipal water but documented in surface water sources. | Sediment filtration, UV, chlorination |
Inorganic Chemicals (25 Contaminants)
Inorganic contaminants include heavy metals, minerals, and radionuclides. Many are naturally occurring but are concentrated by human activities including mining, industrial processes, and agricultural runoff. Heavy metals bioaccumulate and cause chronic toxicity even at low concentrations.
| Contaminant | EPA MCL | Health Effects | Sources | Treatment |
|---|---|---|---|---|
| Lead | 15 ug/L (action level) | Neurodevelopmental damage in children (IQ loss, behavioral problems), kidney damage, hypertension in adults. No safe level identified. | Corrosion of lead pipes, solder, brass fixtures | Reverse osmosis, ion exchange, activated alumina, NSF 53 certified carbon |
| Mercury (inorganic) | 2 ug/L | Kidney damage, neurological effects. Methylmercury (organic form) causes severe neurotoxicity. | Natural deposits, industrial discharge, coal combustion | RO, activated carbon, distillation |
| Arsenic | 10 ug/L | Skin lesions, cardiovascular disease, diabetes, lung/bladder/skin cancer. Carcinogen. | Natural geological deposits, mining runoff, pesticides | RO, activated alumina, ion exchange, distillation |
| Cadmium | 5 ug/L | Kidney damage, bone demineralization (Itai-Itai disease), probable carcinogen. | Corrosion of galvanized pipes, mining, battery manufacturing | RO, ion exchange, coagulation/filtration |
| Chromium (total) | 100 ug/L | Cr(VI) (hexavalent): lung cancer, liver/kidney damage. Cr(III) is less toxic and essential in trace amounts. | Steel/metal plating, leather tanning, natural deposits | RO, ion exchange, coagulation/filtration |
| Copper | 1.3 mg/L | Gastrointestinal distress, liver damage at high doses. Wilson's disease patients especially vulnerable. | Corrosion of copper pipes and plumbing | pH adjustment, corrosion control |
| Iron | 0.3 mg/L (SMCL) | Non-toxic at typical levels. Causes staining, metallic taste, supports bacterial growth. | Natural deposits, corrosion of iron pipes | Oxidation/filtration, ion exchange, greensand |
| Manganese | 0.05 mg/L (health advisory) | Neurological effects at high chronic exposure. Stains fixtures black. | Natural deposits | Oxidation/filtration, ion exchange, greensand |
| Aluminum | 0.05-0.2 mg/L | Possible link to neurological disorders at very high levels. Affects dialysis patients. | Water treatment coagulants, natural deposits | Coagulation/filtration, RO |
| Antimony | 6 ug/L | Increases blood cholesterol, decreases blood sugar. Possible carcinogen. | Fire retardants, ceramics, solder, natural deposits | RO, coagulation/filtration |
| Beryllium | 4 ug/L | Intestinal lesions, cancer risk. Carcinogen. | Metal alloy production, coal combustion, natural deposits | RO, activated alumina, ion exchange |
| Nickel | No MCL | Allergic dermatitis, lung/nasal cancer (inhalation), heart/liver damage at high doses. | Stainless steel/nickel alloy corrosion, natural deposits | RO, ion exchange |
| Silver | 0.1 mg/L | Argyria (permanent blue-gray skin discoloration). Antibacterial at low doses. | Natural deposits, mining, electroplating | Activated carbon, ion exchange |
| Thallium | 2 ug/L | Hair loss, peripheral neuropathy, liver/kidney damage, intestinal damage. | Electronics, glass manufacturing, leaching from ore | Activated alumina, ion exchange |
| Selenium | 50 ug/L | Essential nutrient at low levels. Hair loss, nail changes, neurological symptoms at excess. | Natural deposits, mining, agricultural runoff | Activated alumina, coagulation/filtration, RO |
| Zinc | 5 mg/L (SMCL) | Essential nutrient. Metallic taste, nausea at high levels. | Natural deposits, galvanized pipe corrosion | Activated carbon, ion exchange |
| Fluoride | 4.0 mg/L | Dental fluorosis above 2 mg/L; skeletal fluorosis above 4 mg/L. Benefits at 0.7-1.0 mg/L for dental health. | Water fluoridation, natural geological deposits | Activated alumina, RO, distillation, bone char |
| Nitrate (as N) | 10 mg/L | Methemoglobinemia (blue baby syndrome) in infants under 6 months. Possible link to certain cancers. | Fertilizer runoff, septic systems, livestock waste, sewage | RO, ion exchange, distillation. Not removable by carbon. |
| Nitrite (as N) | 1 mg/L | Same as nitrate; more potent cause of methemoglobinemia. | Same as nitrate; also water distribution system | Same as nitrate |
| Sulfate | 250 mg/L (SMCL) | Laxative effect at high concentrations. Gastrointestinal distress. | Natural deposits, industrial discharge | RO, ion exchange, distillation |
| Chloride | 250 mg/L (SMCL) | Salty taste. Corrosive to plumbing at high levels. | Natural deposits, seawater intrusion, road salt | RO, distillation |
| Sodium | No MCL | Contributes to hypertension in salt-sensitive individuals. EPA advisory: 20 mg/L for sodium-restricted diets. | Water softeners, natural deposits, road salt | RO, distillation |
| Radium-226/228 | 5 pCi/L (combined) | Bone cancer, leukemia. Radioactive; emits alpha and gamma radiation. | Natural geological deposits, especially granite/shale | Ion exchange (strong acid cation), RO, lime softening |
| Uranium | 30 ug/L | Kidney toxicity, cancer risk. Radioactive and chemically toxic. | Natural geological deposits, mining, fertilizer | RO, anion exchange, coagulation/filtration |
| Alpha particles | 15 pCi/L | Cancer risk from internal radiation exposure. Emitted by radioactive decay of uranium, radium. | Natural deposits | RO, ion exchange |
| Beta particles | 4 mrem/yr | Cancer risk. Emitted by radioactive strontium-90, cesium-137. | Natural deposits, fallout from nuclear testing | RO, ion exchange |
Organic Chemicals (30 Contaminants)
Organic contaminants include volatile organic compounds (VOCs) - industrial solvents and fuels that evaporate readily - semi-volatile organic compounds (SVOCs) including pesticides and herbicides, and persistent industrial chemicals. Many are carcinogenic at trace levels and are regulated at microgram-per-liter concentrations.
| Contaminant | EPA MCL | Health Effects | Sources | Treatment |
|---|---|---|---|---|
| Benzene | 5 ug/L | Acute myelogenous leukemia (AML), aplastic anemia. Carcinogen. | Petroleum refining, gasoline storage, industrial discharge | Activated carbon, air stripping, RO, advanced oxidation |
| Toluene | 1 mg/L | Nervous system damage, liver/kidney damage, developmental effects. | Petroleum products, paints, solvents | Activated carbon, air stripping |
| Xylenes | 10 mg/L | Nervous system damage, liver/kidney effects. | Petroleum products, solvents | Activated carbon, air stripping |
| Trichloroethylene (TCE) | 5 ug/L | Liver damage, kidney damage, immunological effects, cancer. Carcinogen. | Metal degreasing, dry cleaning, industrial discharge | Activated carbon, air stripping, UV oxidation |
| Tetrachloroethylene (PCE) | 5 ug/L | Liver damage, cancer. Carcinogen. | Dry cleaning, metal degreasing | Activated carbon, air stripping |
| Carbon tetrachloride | 5 ug/L | Liver damage, kidney damage, cancer. Carcinogen. | Industrial solvents, chemical manufacturing | Activated carbon, air stripping |
| 1,1,1-Trichloroethane | 0.2 mg/L | Liver, nervous system, circulatory effects. | Industrial solvents, metal degreasing | Air stripping, activated carbon |
| 1,2-Dichloroethane | 5 ug/L | Cancer (liver, stomach, pancreas). Carcinogen. | Industrial solvents, leaded gasoline additive | Activated carbon, air stripping |
| 1,1-Dichloroethylene | 7 ug/L | Liver/kidney damage. Carcinogen. | Industrial discharge, plastic manufacturing | Activated carbon, air stripping |
| cis-1,2-Dichloroethylene | 70 ug/L | Liver, nervous system, circulatory effects. | Industrial discharge | Air stripping, activated carbon |
| trans-1,2-Dichloroethylene | 100 ug/L | Liver, nervous system effects. | Industrial discharge | Air stripping, activated carbon |
| Vinyl chloride | 2 ug/L | Liver cancer, nerve damage, immune reactions. Carcinogen. | PVC pipe manufacturing, plastic production | Activated carbon, air stripping |
| MTBE (Methyl tert-butyl ether) | No federal MCL | Potential carcinogen; taste/odor at very low concentrations (5-15 ug/L). | Gasoline additive, leaking storage tanks | Activated carbon, air stripping, advanced oxidation |
| Ethylbenzene | 0.7 mg/L | Liver, kidney, nervous system effects. | Petroleum refining, gasoline | Activated carbon, air stripping |
| Styrene | 0.1 mg/L | Liver, nervous system effects. Possible carcinogen. | Plastic/rubber manufacturing, disposal sites | Activated carbon, air stripping |
| Dichloromethane (Methylene chloride) | 5 ug/L | Liver damage, cancer. Carcinogen. | Paint strippers, pharmaceuticals, metal cleaning | Activated carbon, air stripping |
| Chlorobenzene | 0.1 mg/L | Liver, kidney, nervous system effects. | Chemical manufacturing | Activated carbon, air stripping |
| o-Dichlorobenzene | 0.6 mg/L | Liver, kidney, blood cell damage. | Chemical manufacturing | Activated carbon, air stripping |
| p-Dichlorobenzene | 75 ug/L | Liver, kidney, blood cell damage, anemia. Carcinogen. | Moth repellents, deodorizers, chemical production | Activated carbon, air stripping |
| 1,2,4-Trichlorobenzene | 70 ug/L | Adrenal gland changes. | Herbicide manufacturing, dye carriers | Activated carbon |
| Atrazine | 3 ug/L | Endocrine disruption, reproductive effects, possible carcinogen. Most commonly detected pesticide in U.S. water. | Agricultural herbicide for corn/sorghum | Activated carbon, ozonation |
| 2,4-D | 70 ug/L | Liver, kidney damage, nervous system effects, possible carcinogen. | Lawn/weed herbicide | Activated carbon |
| Glyphosate | 700 ug/L | Probable carcinogen (IARC Group 2A), liver/kidney damage, endocrine disruption. | Roundup and other herbicides | Activated carbon, ozonation, RO |
| Simazine | 4 ug/L | Tremors, reproductive effects, blood toxicity, possible carcinogen. | Agricultural herbicide | Activated carbon |
| Carbofuran | 40 ug/L | Nervous system damage, reproductive effects. | Insecticide for crops | Activated carbon |
| Endrin | 2 ug/L | Liver, kidney, heart damage. | Insecticide (banned in U.S. but persistent) | Activated carbon |
| Lindane | 0.2 ug/L | Liver, kidney, nervous system, immune effects. Carcinogen. | Insecticide (banned in U.S. but persistent) | Activated carbon |
| Methoxychlor | 40 ug/L | Reproductive damage, liver/kidney/nerve effects. | Insecticide (banned) | Activated carbon |
| Toxaphene | 3 ug/L | Kidney, liver, thyroid damage, cancer. Carcinogen. | Insecticide (banned) | Activated carbon |
| Dioxin (2,3,7,8-TCDD) | 3x10^-8 ug/L | Cancer, reproductive/developmental effects, immune damage, endocrine disruption. Extremely toxic. | Incineration, chemical manufacturing, paper bleaching | Activated carbon, RO |
| PCBs (Polychlorinated biphenyls) | 0.5 ug/L | Cancer, reproductive/developmental effects, immune damage, thyroid effects. Carcinogen. | Industrial coolants/lubricants (banned) | Activated carbon, RO |
Disinfection Byproducts (8 Contaminants)
Disinfection byproducts (DBPs) form when chlorine or other disinfectants react with naturally occurring organic matter in water. They represent an ironic trade-off: water disinfection prevents infectious disease but creates chronic chemical exposure risks. Over 600 DBP species have been identified; the EPA regulates the most prevalent groups.
| Contaminant | EPA MCL | Health Effects | Treatment |
|---|---|---|---|
| Total Trihalomethanes (TTHMs) | 80 ug/L | Bladder cancer, colorectal cancer, reproductive effects (miscarriage, birth defects). Group includes chloroform, bromodichloromethane, dibromochloromethane, bromoform. | Activated carbon, catalytic carbon, RO, UV/advanced oxidation |
| Haloacetic Acids (HAA5) | 60 ug/L | Cancer, reproductive effects. Group includes monochloroacetic acid, dichloroacetic acid, trichloroacetic acid, monobromoacetic acid, dibromoacetic acid. | Activated carbon, catalytic carbon, RO |
| Bromate | 10 ug/L | Cancer. Forms when ozone disinfects water containing bromide. | Activated carbon, ferrous iron reduction, UV |
| Chlorite | 1.0 mg/L | Anemia in infants and fetuses, nervous system effects. Byproduct of chlorine dioxide disinfection. | Activated carbon, reducing agents |
| Chloroform | Part of TTHMs | Cancer, liver/kidney damage. Most prevalent individual THM. | Activated carbon, air stripping |
| Bromodichloromethane | Part of TTHMs | Cancer, liver/kidney damage. Most carcinogenic individual THM. | Activated carbon, air stripping |
| Dichloroacetic acid | Part of HAA5 | Cancer, liver damage, reproductive effects. | Activated carbon, UV oxidation |
| Trichloroacetic acid | Part of HAA5 | Cancer, reproductive effects. | Activated carbon, UV oxidation |
PFAS Compounds (10 Contaminants)
Per- and polyfluoroalkyl substances (PFAS) are a class of over 4,700 synthetic chemicals used since the 1940s for water, grease, and stain resistance. They are extremely persistent in the environment and human body ("forever chemicals"). EPA issued health advisories in 2022 and is developing enforceable MCLs.
Regulatory Status Update (2026)
EPA established enforceable MCLs for PFOA and PFOS at 4 ng/L (ppt) each in 2024. Four additional PFAS (PFHxS, PFNA, PFBS, GenX) have a hazard index MCL. These are among the most stringent drinking water standards ever set. Utilities nationwide are scrambling to install treatment.
| Contaminant | EPA MCL / HA | Health Effects | Sources | Treatment |
|---|---|---|---|---|
| PFOA (Perfluorooctanoic acid) | 4 ng/L (MCL, 2024) | Cancer (kidney, testicular), thyroid disease, ulcerative colitis, high cholesterol, pregnancy-induced hypertension, developmental effects. | Teflon production, firefighting foam, stain repellents, waterproofing | Activated carbon (GAC), anion exchange, RO, ion exchange resins |
| PFOS (Perfluorooctanesulfonic acid) | 4 ng/L (MCL, 2024) | Cancer, thyroid disease, immune suppression, high cholesterol, developmental effects. More bioaccumulative than PFOA. | Firefighting foam (AFFF), stain repellents, chrome plating | Activated carbon (GAC), anion exchange, RO |
| PFHxS (Perfluorohexanesulfonic acid) | 10 ng/L (HA) | Thyroid disease, immune effects, developmental toxicity. | Firefighting foam, chrome plating | Anion exchange, activated carbon, RO |
| PFNA (Perfluorononanoic acid) | 10 ng/L (HA) | Liver damage, developmental effects, immune effects. | Industrial processes, fluoropolymer production | Anion exchange, activated carbon, RO |
| GenX (HFPO-DA) | 10 ng/L (HA) | Liver, kidney, thyroid, immune, developmental, cancer. Replacement for PFOA. | Teflon manufacturing | Anion exchange, RO, advanced oxidation |
| PFBS (Perfluorobutanesulfonic acid) | 2000 ng/L (HA) | Thyroid, kidney, reproductive effects. Less bioaccumulative than longer-chain PFAS. | Replacement chemistry for PFOS | Activated carbon, anion exchange |
| PFDA | No MCL | Liver damage, developmental effects. | Industrial uses | Anion exchange, RO |
| PFUnA | No MCL | Liver toxicity, developmental effects. | Industrial uses | Anion exchange, RO |
| PFDoA | No MCL | Similar toxicity profile to other long-chain PFAS. | Industrial uses | Anion exchange, RO |
| PFBA (Perfluorobutanoic acid) | No MCL | Thyroid, developmental effects. Short-chain; removed less effectively by carbon. | Industrial uses | RO, anion exchange |
Physical & Aesthetic Parameters (10)
Physical and aesthetic parameters do not typically pose direct health risks but affect water usability, plumbing longevity, and treatment effectiveness. Some, like turbidity and pH, serve as important indicators of overall water quality.
| Parameter | EPA Standard | Significance | Treatment |
|---|---|---|---|
| Turbidity | TT (0.3-1 NTU) | Cloudiness from suspended particles. Indicator of filtration effectiveness and microbial risk. Regulated as a treatment technique. | Sediment filtration, coagulation, media filtration |
| Color | 15 color units (SMCL) | Aesthetic concern. Caused by dissolved organic matter (tannins, humic acids), metals, or algae. | Activated carbon, ion exchange, coagulation |
| Total Dissolved Solids (TDS) | 500 mg/L (SMCL) | Measure of all dissolved inorganic salts. Affects taste; high TDS indicates need for RO or distillation. | RO, distillation, deionization |
| Hardness (as CaCO3) | No MCL | Calcium and magnesium content. Causes scale buildup, soap scum, appliance damage. No health risk at typical levels. | Water softener (ion exchange), reverse osmosis |
| pH | 6.5 - 8.5 (SMCL) | Acidity/alkalinity. Below 6.5: corrosive to pipes (lead/copper leaching). Above 8.5: bitter taste, scale formation. | Acid neutralizer (raise pH), acid injection (lower pH) |
| Temperature | No standard | Affects treatment effectiveness, microbial growth rate, and taste. Legionella grows in 77-108-F water. | Temperature management |
| Conductivity | No standard | Measure of water's ability to conduct electricity; correlates with TDS. Useful for monitoring RO performance. | Same as TDS |
| Corrosivity (Langelier Index) | No MCL | Tendency to dissolve metals from pipes. Negative LSI = corrosive (risk of lead/copper release). | pH adjustment, alkalinity addition, corrosion inhibitors |
| Alkalinity | No MCL | Buffering capacity against pH changes. Low alkalinity = unstable pH, corrosive water. High alkalinity = high pH. | Acid neutralizer filter (adds alkalinity) |
| Total Organic Carbon (TOC) | TT (no number) | Measure of organic matter. Precursor for DBP formation when chlorinated. Regulated as treatment technique. | Activated carbon, coagulation, UV oxidation |
Emerging Contaminants (20)
Emerging contaminants are substances detected in water supplies that are not currently regulated by the EPA but are under investigation for potential health effects. They include pharmaceuticals, personal care products, industrial chemicals, and novel pollutants. Detection does not imply health risk at the concentrations typically found, but the presence raises questions about long-term, low-dose effects.
| Contaminant | Category | Health Concerns | Sources | Treatment |
|---|---|---|---|---|
| Ibuprofen | Pharmaceutical | Endocrine disruption at environmental concentrations; aquatic toxicity. | Human excretion, pharmaceutical manufacturing | RO, advanced oxidation, activated carbon (limited) |
| Acetaminophen | Pharmaceutical | Liver toxicity at high doses; environmental effects unknown at trace levels. | Human excretion | RO, advanced oxidation |
| Aspirin | Pharmaceutical | Environmental toxicity to aquatic organisms. | Human excretion | RO, advanced oxidation |
| Antibiotics (various) | Pharmaceutical | Antibiotic resistance development. Bacteria exposed to sub-lethal concentrations may develop resistance. | Agricultural use, human excretion, hospital discharge | RO, UV/advanced oxidation, ozone |
| Hormones (estrone, estriol, 17-beta estradiol) | Pharmaceutical | Endocrine disruption, feminization of male fish documented. Potential human effects under study. | Human excretion, livestock operations | RO, activated carbon, advanced oxidation |
| Birth control hormones (ethinyl estradiol) | Pharmaceutical | Endocrine disruption; potent at nanogram-per-liter concentrations. | Human excretion | RO, activated carbon, advanced oxidation |
| Antidepressants (fluoxetine, sertraline) | Pharmaceutical | Behavioral effects in aquatic life. Human health effects at trace levels unknown. | Human excretion | RO, advanced oxidation |
| Lipid regulators (gemfibrozil, bezafibrate) | Pharmaceutical | Ecotoxicity; potential endocrine effects. | Human excretion | RO, advanced oxidation |
| Microplastics | Novel pollutant | Unknown human health effects. Particle size, shape, and polymer type determine potential risk. Physical ingestion concerns. | Plastic breakdown, synthetic textile washing, cosmetic microbeads | Filtration (sub-micron), ultrafiltration, RO |
| Nanoparticles (TiO2, Ag, ZnO) | Novel pollutant | Unknown. Potential for cellular uptake and oxidative stress depending on size and coating. | Consumer products, sunscreens, antimicrobial coatings | Ultrafiltration, RO |
| Perchlorate | Industrial/military | Thyroid disruption - interferes with iodide uptake. Impairs fetal/infant brain development. | Rocket fuel, fireworks, flares, Chilean fertilizer | RO, ion exchange (specialty resins), activated carbon (limited) |
| 1,4-Dioxane | Industrial solvent | Liver, kidney damage, cancer. Carcinogen. Highly mobile in groundwater; does not adsorb well to carbon. | Industrial solvent, byproduct of ethoxylation (detergents, cosmetics) | Advanced oxidation (UV/H2O2, ozone), RO (partial) |
| NDMA (N-Nitrosodimethylamine) | Disinfection/industrial byproduct | Liver cancer. Extremely potent carcinogen. Forms during chloramination and chlorination of wastewater-impacted sources. | Industrial chemical, chloramination byproduct, rocket fuel | UV photolysis, RO (partial) |
| Chromium-6 (hexavalent) | Metal | Lung cancer (inhalation), stomach cancer, liver/kidney damage. EPA reviewing separate MCL. California MCL: 10 ug/L. | Steel production, chrome plating, leather tanning, natural deposits | RO, ion exchange, reduction to Cr(III) + precipitation |
| Manganese (neurotoxicity concern) | Mineral | Neurological effects (manganism) similar to Parkinson's disease at chronic elevated exposure. Infant formula preparation concern. | Natural deposits | Oxidation/filtration, ion exchange |
| Boron | Mineral | Reproductive/developmental toxicity at high doses. | Detergents, natural deposits, mining | RO, ion exchange |
| Vanadium | Metal | Kidney damage, neurological effects, respiratory irritation. | Natural deposits, fossil fuel combustion | RO, anion exchange |
| Strontium | Metal | Bone health concern (incorporates into bone). Radioactive Sr-90 is a cancer risk. | Natural deposits, nuclear fallout | RO, lime softening, ion exchange |
| DEET | Personal care product | Nervous system effects at high doses. Environmental persistence. | Insect repellent runoff | Activated carbon, RO |
| Triclosan | Personal care product | Endocrine disruption, antibiotic resistance, environmental toxicity. Banned in hand soaps but still in other products. | Antibacterial soaps, toothpaste, cosmetics | Activated carbon, UV oxidation |
Treatment Technology Reference
Use this quick-reference guide to identify which filtration technologies address your specific contamination concerns. For comprehensive protection, many systems combine multiple technologies.
| Technology | Effective Against | Not Effective Against | Typical Application |
|---|---|---|---|
| Activated Carbon (GAC) | Chlorine, VOCs, pesticides, herbicides, taste/odor, some PFAS | Dissolved minerals, nitrates, fluoride, arsenic, bacteria, salts | Whole-house, under-sink, pitcher, faucet filters |
| Catalytic Carbon | Chlorine, chloramine, VOCs, pesticides, some PFAS | Dissolved minerals, nitrates, fluoride, salts | Whole-house systems (chloramine-specific) |
| Reverse Osmosis (RO) | Lead, arsenic, fluoride, nitrates, TDS, bacteria, viruses, cysts, most organic chemicals | Chlorine (damages membrane; needs carbon pre-filter), dissolved gases | Under-sink point-of-use systems |
| UV Disinfection | Bacteria, viruses, cysts (Giardia, Cryptosporidium) | Chemical contaminants, dissolved minerals, metals, taste/odor | Whole-house microbiological protection, well water |
| Ion Exchange | Hardness minerals, radium, uranium, nitrate, perchlorate, heavy metals | Bacteria, viruses, organic chemicals, chlorine | Water softeners, specialty contaminant removal |
| Activated Alumina | Fluoride, arsenic, selenium | Bacteria, organic chemicals, hardness, most metals | Fluoride/arsenic removal cartridges |
| Distillation | Bacteria, viruses, cysts, dissolved minerals, TDS, metals, nitrates, fluoride | VOCs (some evaporate with steam; carbon post-filter needed) | Countertop distillers |
| Anion Exchange | PFAS, uranium, perchlorate, nitrate, chromium-6 | Hardness minerals (cations), bacteria, organic chemicals | Specialty PFAS treatment systems |
| Sediment Filtration | Sand, silt, rust, particulates, cysts (at 1 micron) | Dissolved chemicals, metals, bacteria smaller than pore size | Pre-filtration for all system types |
| Advanced Oxidation (UV/H2O2, Ozone) | 1,4-dioxane, NDMA, pharmaceuticals, VOCs, DBP precursors, most organic chemicals | Dissolved minerals, salts, TDS | Municipal treatment, remediation systems |
Our Methodology
Every product on Filter Tested undergoes 4-6 months of research-based analysis in real-world conditions. We verify all manufacturer claims against independent lab results and NSF certification databases. Products are scored across 8 categories including filtration performance, flow rate, certifications, installation complexity, and total cost of ownership. Learn more about how we test.
Frequently Asked Questions
How do I know which contaminants are in my water?
Start by reading your water utility's annual Consumer Confidence Report (CCR), which lists all contaminants tested and their concentrations. The CCR is mailed to customers annually and is also available on your utility's website. For private wells, you must conduct your own testing through a certified laboratory. We recommend the EPA's certified laboratory list (epa.gov) or state health department resources. For targeted concerns - such as lead from household plumbing - test the water at your tap rather than relying on utility-level data, which represents the water leaving the treatment plant, not your faucet.
What is the difference between an MCL and a health advisory?
An MCL (Maximum Contaminant Level) is an enforceable legal limit set by the EPA under the Safe Drinking Water Act. Public water systems must ensure their water does not exceed these limits. A health advisory is a non-enforceable, non-regulatory guideline that provides information on contaminants that can cause human health effects but for which no formal regulation yet exists. Health advisories are typically more conservative than eventual MCLs and reflect the latest science. For example, PFAS had health advisories for years before enforceable MCLs were established in 2024.
Should I be worried about emerging contaminants in my water?
The presence of emerging contaminants at the trace levels typically detected does not necessarily indicate an immediate health risk. Most emerging contaminants are found at concentrations thousands of times below therapeutic doses. However, the long-term, low-dose effects of chronic exposure to complex mixtures of chemicals are not well understood. The prudent approach is to use a water treatment system that provides broad-spectrum removal - reverse osmosis with carbon pre-filtration removes the widest range of contaminants including most pharmaceuticals, PFAS, and organic chemicals. If you have specific concerns, targeted testing is the first step.
Does boiling water remove contaminants?
Boiling water kills bacteria, viruses, and protozoan cysts, making it an effective emergency disinfection method. However, boiling does NOT remove chemical contaminants - in fact, it concentrates non-volatile chemicals such as lead, nitrates, arsenic, and dissolved salts because water evaporates while contaminants remain. Volatile organic compounds may partially evaporate with steam, but this is unreliable and depends on the specific chemical. For chemical contaminant removal, filtration is required.
What is the best treatment system for well water?
Well water treatment must be tailored to the specific contaminants present. Start with a comprehensive water test covering bacteria, nitrates, arsenic, lead, iron, manganese, hardness, pH, and VOCs. Common well water treatment configurations include: (1) Sediment filter + water softener (for hard water with iron/manganese), (2) Sediment filter + UV disinfection (for microbiological safety), (3) Sediment filter + iron filter + water softener + UV (comprehensive), (4) Add RO for drinking water (removes arsenic, nitrates, fluoride, metals). There is no one-size-fits-all well water system - treatment must be based on test results.
How do PFAS get into drinking water?
PFAS enter drinking water through multiple pathways: industrial discharge from manufacturing facilities, leaching from firefighting foam (AFFF) used at military bases and airports, landfill leachate containing consumer products, wastewater treatment plant effluent, and atmospheric deposition. Certain areas have known high concentrations near industrial facilities, military bases, and airports. If you live within a few miles of these sites, testing for PFAS is advisable. Treatment with granular activated carbon (GAC), anion exchange resins, or reverse osmosis is effective.
What are disinfection byproducts and why do they matter?
Disinfection byproducts (DBPs) form when chlorine or other disinfectants react with naturally occurring organic matter in water. The two most significant groups are trihalomethanes (TTHMs) and haloacetic acids (HAA5), both classified as probable or possible carcinogens. DBPs represent a trade-off: without disinfection, waterborne disease would cause widespread illness; with disinfection, chronic DBP exposure increases long-term cancer risk. The EPA regulates DBP levels, and many utilities now use alternative disinfection methods or enhanced organic matter removal to minimize DBP formation. Home treatment with activated carbon or catalytic carbon reduces DBPs in drinking water.