Reference
Drinking water contaminant glossary
A plain-language reference for the contaminants regulated under the federal Safe Drinking Water Act. Each entry lists the contaminant’s legal limit, its health goal, the reporting unit, and what long-term exposure is associated with — sourced from EPA and state primacy-agency documentation.
27 contaminants across 8 categories.
MCL vs. MCLG — two different numbers
- MCL — Maximum Contaminant Level
- The enforceable legal limit a utility may not exceed. It is set as close to the health goal as is feasible given available treatment technology and cost.
- MCLG / health goal — Maximum Contaminant Level Goal
- The non-enforceable level below which there is no known or expected health risk. For carcinogens such as lead, arsenic, and several PFAS, the health goal is 0 — meaning no exposure is considered risk-free, even when a system is legally compliant.
Metal
8 contaminantsLead
PB90Delays in physical and mental development in infants and children; kidney problems and high blood pressure in adults.
15 µg/L MCLGoal: 0 (no safe level)Hexavalent Chromium
CR6Known human carcinogen linked to stomach, lung, and nasal cancers with long-term ingestion.
10 µg/L MCLGoal: 0.020 µg/LArsenic
1005Skin damage and circulatory problems; long-term exposure increases bladder, lung, and skin cancer risk (MCLG = 0).
10 µg/L MCLGoal: 0 (no safe level)Copper
CU90Short-term gastrointestinal distress; long-term liver or kidney damage above the action level.
1.3 mg/L MCLGoal: 1.3 mg/LTotal Chromium
1020Allergic dermatitis in sensitive individuals; total chromium includes carcinogenic hexavalent and trivalent forms.
100 µg/L MCLGoal: 100 µg/LBarium
1010Increases blood pressure at elevated levels.
2 mg/L MCLGoal: 2 mg/LCadmium
1015Kidney damage with long-term exposure; can leach from galvanized pipe and fittings.
0.0050 mg/L MCLGoal: 0.0050 mg/LMercury (inorganic)
1035Kidney damage and nervous-system effects above the MCL.
0.0020 mg/L MCLGoal: 0.0020 mg/L
Inorganic
3 contaminantsNitrate
1040Causes methemoglobinemia ("blue-baby syndrome") in infants under 6 months.
10 mg/L MCLGoal: 10 mg/LNitrite
1041Causes methemoglobinemia in infants; acutely dangerous.
1 mg/L MCLGoal: 1 mg/LFluoride
1925Dental and skeletal fluorosis with long-term exposure above the MCL; secondary standard is 2 mg/L.
4 mg/L MCLGoal: 4 mg/L
PFAS
6 contaminantsPFOA
PFOACancer, thyroid disease, immune and developmental effects.
4 ng/L MCLGoal: 0 (no safe level)PFOS
PFOSLiver and thyroid harm, immune suppression, increased cancer risk.
4 ng/L MCLGoal: 0 (no safe level)GenX (HFPO-DA)
GENXDevelopmental toxicity, liver damage, and immune disruption.
10 ng/L MCLGoal: 10 ng/LPFHxS
PFHXSThyroid and immune effects; regulated under the EPA PFAS hazard-index mixture rule.
10 ng/L MCLGoal: 10 ng/LPFNA
PFNALiver toxicity and developmental effects; regulated under the EPA PFAS hazard-index mixture rule.
10 ng/L MCLGoal: 10 ng/LPFBS
6590Thyroid effects; part of the PFAS mixture hazard-index rule.
No federal MCLGoal: 0 (no safe level)
DBP
2 contaminantsVOC
3 contaminantsBenzene
2990Anemia and decreased blood platelets; long-term exposure raises leukemia risk (MCLG = 0).
5 µg/L MCLGoal: 0 (no safe level)Trichloroethylene
2984Liver damage and increased cancer risk; industrial degreaser (MCLG = 0).
5 µg/L MCLGoal: 0 (no safe level)Tetrachloroethylene
2987Liver problems and increased cancer risk; dry-cleaning and industrial solvent (MCLG = 0).
5 µg/L MCLGoal: 0 (no safe level)