Private Well Water: Testing, Treatment & Contamination (2026)
13M US households drink from unregulated private wells. CDC testing schedule, common contaminants by region, treatment systems, and PFAS in well water.
Reviewed by Dr. Marcus Reilly, PhD – PFAS & Drinking Water Scientist
Quick Answer
Private wells are not regulated by the EPA. About 23% have at least one contaminant above a health-based benchmark per USGS. The CDC recommends testing every 12 months for total coliform and nitrate, every 2-3 years for a full chemistry panel (arsenic, lead, fluoride, sulfate, manganese, hardness, pH, TDS). Test for PFAS once if you are within 5 miles of a known industrial source, military base, or AFFF release site.
Key facts
- US households on private wells
- approximately 13 million
- Private wells with at least one contaminant above health benchmark
- approximately 23% (USGS estimate)
- Wells exceeding EPA arsenic limit (10 ppb)
- approximately 7% nationally
- CDC-recommended bacteria + nitrate test cadence
- every 12 months
- CDC-recommended full chemistry panel cadence
- every 2-3 years
Frequently asked questions
Is well water safer than city water?
It depends entirely on testing discipline. EPA regulates ~155,000 public water systems with mandatory testing. Private wells (about 13 million US homes) are completely unregulated. With CDC-recommended testing well water can be cleaner than city water; without it, contamination can persist for years undetected.
How often should I test my well water?
CDC recommendations: every 12 months for total coliform bacteria and nitrate, every 2-3 years for a full chemistry panel (arsenic, lead, fluoride, sulfate, manganese, hardness, pH, TDS). Test sooner after flooding within 1/4 mile, septic repairs, or neighbor-reported contamination.
What filter do I need for well water?
Whole-house filtration is essential because contaminants vary across uses. A typical setup: sediment pre-filter, water softener if hardness exceeds 7 grains per gallon, UV disinfection if bacteria has tested positive, and a reverse osmosis system at the kitchen sink for drinking water.