What Do My Well Water Test Results Mean?

How to read your lab report

• ND or <0.5 — not detected or below the detection limit. Good result.
• µg/L or ppb — micrograms per liter = parts per billion. These are the same unit.
• mg/L or ppm — milligrams per liter = parts per million. 1 mg/L = 1,000 µg/L.
• pCi/L — picocuries per liter. Used for radioactive contaminants like radon and radium.
• CFU/100mL — colony forming units per 100 mL. Used for bacteria (E. coli, total coliform).

The EPA limit shown in your result is the Maximum Contaminant Level (MCL) — the enforceable standard for public water systems. Private wells are not regulated, so testing is your responsibility.

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