Substances, toxicology & benchmarks
Contaminant Directory
Comprehensive reference on chemical analytes, health benchmarks, statutory limits, and certified reduction methods.
19 of 29 substances have city results or violations in PurityMap’s record.
5 substances
PFAS chemicals family overview →PFAS chemicals
Synthetic “forever chemicals”. Several now have federal limits; each compound has its own.
PFOAPerfluorooctanoic acid640 cities above the federal limit · of 3,748 with a result4 ng/LMCLEnforceable 2029 · MCLG 0Reverse osmosisActivated carbon (GAC)Anion exchangeCAS 335-67-1Understand →PFOSPerfluorooctanesulfonic acid658 cities above the federal limit · of 3,748 with a result4 ng/LMCLEnforceable 2029 · MCLG 0Reverse osmosisActivated carbon (GAC)Anion exchangeCAS 1763-23-1Understand →PFHxSPerfluorohexanesulfonic acid76 cities above the federal limit · of 3,748 with a result10 ng/LMCLReverse osmosisActivated carbon (GAC)Anion exchangeCAS 355-46-4Understand →GenX (HFPO-DA)Hexafluoropropylene oxide dimer acid (HFPO-DA)6 cities above the federal limit · of 20 with a detection10 ng/LMCLAlso in the PFAS hazard index · MCLG 10 ng/LReverse osmosisActivated carbon (GAC)Anion exchangeCAS 62037-80-3Understand →PFNAPerfluorononanoic acid8 cities above the federal limit · of 32 with a detection10 ng/LMCLAlso in the PFAS hazard index · MCLG 10 ng/LReverse osmosisActivated carbon (GAC)Anion exchangeCAS 375-95-1Understand →
9 substances
Heavy metals family overview →Heavy metals
Most enter from natural deposits or from pipes and plumbing on the way to the tap.
LeadLead (Pb)16 cities above the action level · of 3,742 with a result15 µg/LAction level90th percentile · MCLG 0 · A treatment trigger, not an MCLReverse osmosisNSF/ANSI 53 lead-certified filtersReplacing lead service linesCAS 7439-92-1Understand →ArsenicArsenic (As)10 cities with a published value · 16 cities with a violation10 µg/LMCLMCLG 0Reverse osmosisAnion exchangeActivated alumina / adsorptive mediaCAS 7440-38-2Understand →Chromium-6Hexavalent chromium (Cr-VI)No city results yetNoneNo federal limitNo separate federal MCL; total chromium MCL is 100 µg/LReverse osmosisAnion exchangeReduction / filtration systemsCAS 18540-29-9Understand →CopperCopper (Cu)47 of 72 cities above the action level1.3 mg/LAction level90th percentile · MCLG 1.3 mg/L · A treatment trigger, not an MCLReverse osmosisCorrosion-control / pH adjustmentFlushing standing water before useCAS 7440-50-8Understand →BariumBarium (Ba)No city results yet2 mg/LMCLMCLG 2 mg/LReverse osmosisIon exchange (softening)ElectrodialysisCAS 7440-39-3Understand →SeleniumSelenium (Se)No city results yet50 µg/LMCLMCLG 0.05 mg/LReverse osmosisAnion exchangeActivated aluminaCAS 7782-49-2Understand →CadmiumCadmium (Cd)1 city with a violation · federal record, since 20165 µg/LMCLMCLG 5 µg/LReverse osmosisIon exchangeActivated carbon (some configurations)CAS 7440-43-9Understand →MercuryInorganic mercury (Hg)No city results yet2 µg/LMCLMCLG 2 µg/LReverse osmosisActivated carbon (GAC)Coagulation / filtrationCAS 7439-97-6Understand →AntimonyAntimony (Sb)No city results yet6 µg/LMCLMCLG 6 µg/LReverse osmosisCoagulation / filtrationCAS 7440-36-0Understand →
3 substances
Disinfection by-products family overview →Disinfection by-products
Formed when disinfectants react with natural organic matter, plus the disinfectant residual itself.
Total trihalomethanes (TTHM)Trihalomethanes59 cities with a detection · of 59 with a result80 µg/LMCLActivated carbonReverse osmosisUnderstand →Haloacetic acids (HAA5)Haloacetic acids (five)58 cities with a detection · of 58 with a result60 µg/LMCLActivated carbonReverse osmosisUnderstand →ChlorineFree chlorine / chloramine residualNo city results yet4 mg/LMRDLAs chlorine (Cl₂)Activated carbonCatalytic carbon (for chloramine)Understand →
3 substances
Inorganics & nitrates family overview →Inorganics & nitrates
Dissolved minerals and nutrients, often from fertiliser, septic systems or natural geology.
NitrateNitrate (as N)22 cities with a published value · 20 cities with a violation10 mg/LMCLAs nitrogenReverse osmosisAnion exchangeDistillationCAS 14797-55-8Understand →FluorideFluoride ion (F−)25 cities with a published value · 8 cities with a violation4.0 mg/LMCLMCLG 4.0 mg/LReverse osmosisActivated alumina / adsorptive mediaDistillationCAS 16984-48-8Understand →NitriteNitrite (as N)4 cities with a violation · federal record, since 20161 mg/LMCLAs nitrogen · MCLG 1 mg/LReverse osmosisAnion exchangeDistillationCAS 14797-65-0Understand →
3 substances
Radionuclides family overview →Radionuclides
Naturally occurring radioactive elements dissolved from rock and soil.
UraniumUranium (U)1 city with a violation · federal record, since 201630 µg/LMCLMCLG 0Reverse osmosisAnion exchangeCoagulation / filtrationCAS 7440-61-1Understand →Radium (226 + 228)Combined radium-226 and radium-22820 cities with a violation · federal record, since 20165 pCi/LMCLRadium-226 + 228 combined · MCLG 0Reverse osmosisIon exchange (softening)Activated aluminaUnderstand →Gross alpha particlesGross alpha particle activity14 cities with a violation · federal record, since 201615 pCi/LMCLExcluding radon and uranium · MCLG 0Reverse osmosisIon exchangeActivated aluminaUnderstand →
4 substances
Volatile organic compounds family overview →Volatile organic compounds
Industrial solvents and fuel components that reach groundwater from spills and discharge.
BenzeneBenzeneNo city results yet5 µg/LMCLMCLG 0Activated carbon (GAC)Packed-tower aeration (air stripping)Reverse osmosisCAS 71-43-2Understand →Trichloroethylene (TCE)Trichloroethylene1 city with a violation · federal record, since 20165 µg/LMCLMCLG 0Activated carbon (GAC)Packed-tower aeration (air stripping)Reverse osmosisCAS 79-01-6Understand →Tetrachloroethylene (PCE)Tetrachloroethylene (perchloroethylene)No city results yet5 µg/LMCLMCLG 0Activated carbon (GAC)Packed-tower aeration (air stripping)Reverse osmosisCAS 127-18-4Understand →Vinyl chlorideVinyl chloride (chloroethene)No city results yet2 µg/LMCLMCLG 0Packed-tower aeration (air stripping)Activated carbon (GAC)Reverse osmosisCAS 75-01-4Understand →
2 substances
Characteristics family overview →Characteristics
Properties of water, or unregulated substances, with no federal health limit.
Hard waterCalcium and magnesium hardness43 cities with a published valueNoneNo federal limitIon-exchange water softenerSalt-free conditionerReverse osmosis (point-of-use)Understand →MicroplasticsMicroplastic particles (< 5 mm)No city results yetNoneNo federal limitNo federal drinking-water limit (unregulated as of 2026)Reverse osmosisNanofiltrationFine activated-carbon block filtrationUnderstand →
Next step
See which of these your system reported.
A benchmark only means something next to a measurement. Your water system’s record shows what was tested, what was found, and what wasn’t monitored.