Groundwater
Water 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.
How It Works
Groundwater is naturally filtered as it percolates through soil and rock, which removes many pathogens and particles. This natural filtration means groundwater generally requires less treatment than surface water. However, groundwater is vulnerable to contamination from nitrate (agricultural fertilizer), PFAS (from firefighting foam), volatile organic compounds (from industrial operations), arsenic (naturally occurring in certain geologies), and septic system leachate. Once contaminated, groundwater is extremely difficult and expensive to clean up because contaminants move slowly through underground aquifers. Private wells, which tap groundwater exclusively, are particularly vulnerable because they are not regulated under the Safe Drinking Water Act.
Related Terms
- Surface Water — Water 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.
- Nitrate — A 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.
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About This Definition
This definition is part of the IsWaterSafe Drinking Water Safety Glossary — 22 terms explaining water contaminants, treatment methods, and safety standards. Written for homeowners, renters, journalists, and public health professionals.