Drinking Water Safety Glossary
Plain-language definitions of drinking water contaminants, treatment methods, EPA standards, and water safety terms. 22 terms and counting.
Common Contaminants
Disinfection Byproducts (DBPs)Chemical compounds formed when disinfectants (chlorine, chloramine) react with natural organic matter in water — including trihalomethanes (THMs) and haloacetic acids (HAAs), linked to cancer and reproductive issues.Lead in Drinking WaterLead contamination from aging pipes, solder, and fixtures — there is no safe level of lead exposure, and even low levels can cause irreversible developmental damage in children.NitrateA contaminant from agricultural runoff and septic systems that is especially dangerous for infants — causing "blue baby syndrome" (methemoglobinemia) at levels above 10 mg/L.PFAS (Forever Chemicals)Per- and polyfluoroalkyl substances — a class of thousands of synthetic chemicals that don't break down in the environment, accumulate in the human body, and are linked to cancer, immune disorders, and developmental problems.PFOA (Perfluorooctanoic Acid)A specific PFAS compound formerly used in Teflon manufacturing — linked to kidney cancer, testicular cancer, thyroid disease, and high cholesterol. The EPA set a drinking water limit of 4 parts per trillion.PFOS (Perfluorooctane Sulfonic Acid)A PFAS compound historically used in Scotchgard, firefighting foam, and industrial applications — linked to cancer and immune system damage. EPA drinking water limit: 4 parts per trillion.
Water Quality Standards
Action LevelA regulatory threshold that triggers required treatment or other corrective action when exceeded — used for lead (15 ppb) and copper (1.3 mg/L) instead of a traditional MCL.Maximum Contaminant Level (MCL)The highest level of a contaminant allowed in drinking water — set by the EPA and enforceable by law. Exceeding the MCL triggers a health-based violation.Maximum Contaminant Level Goal (MCLG)The level of a contaminant in drinking water below which there is no known or expected health risk — a non-enforceable goal that is often stricter than the enforceable MCL.Water Safety ScoreIsWaterSafe's proprietary A-F grade for water systems, based on health violations (40%), contaminant exceedances (30%), enforcement history (20%), and monitoring compliance (10%).
Water Treatment
Activated Carbon FiltrationA water treatment method using porous carbon material to adsorb contaminants — effective for removing chlorine, many organic chemicals, some PFAS, and improving taste and odor.ChlorinationThe most common method of disinfecting drinking water — adding chlorine or chloramine to kill bacteria, viruses, and parasites before water reaches your tap.Reverse Osmosis (RO)A water treatment process that forces water through a semipermeable membrane to remove up to 99% of contaminants — including lead, PFAS, nitrate, arsenic, and most other dissolved substances.
Testing & Reporting
Consumer Confidence Report (CCR)An annual water quality report that every public water system must send to customers — showing which contaminants were detected, at what levels, and whether any violations occurred.Health-Based ViolationThe most serious type of drinking water violation — indicating that water quality has exceeded a maximum contaminant level or failed to meet a treatment requirement that directly protects health.SDWIS (Safe Drinking Water Information System)The EPA database that tracks every public water system in the United States — violations, enforcement actions, contaminant levels, and system characteristics.
Regulation & Oversight
Environmental Protection Agency (EPA)The federal agency that sets drinking water standards, regulates public water systems, and publishes the data that IsWaterSafe uses to assess water safety.Safe Drinking Water Act (SDWA)The primary federal law governing drinking water quality — authorizing the EPA to set standards for contaminants in public water systems and requiring states to enforce those standards.
Health & Water Sources
Boil Water AdvisoryA public health notice requiring residents to boil tap water before drinking or cooking — issued when water may be contaminated with disease-causing organisms.GroundwaterWater found underground in aquifers — the drinking water source for about half of all Americans and nearly all rural residents, generally cleaner than surface water but vulnerable to contamination from agriculture and industry.Private WellA water supply serving a single household — not regulated by the EPA or the Safe Drinking Water Act. About 43 million Americans rely on private wells and are responsible for their own water testing.Surface WaterWater from rivers, lakes, and reservoirs — the drinking water source for the majority of large cities. Surface water requires more intensive treatment than groundwater because it is more exposed to contamination.