EPA Drinking Water Standards Explained: MCLs for Well Owners

What Are MCLs?

Maximum Contaminant Levels (MCLs) are legally enforceable standards that public water systems must meet. While MCLs do not legally apply to private wells, they provide the best available benchmark for safe drinking water levels.

Key MCLs for Well Owners

Arsenic: 10 ppb. Lead: 15 ppb (action level). Nitrate: 10 mg/L. PFOS/PFOA: 4 ppt. Coliform bacteria: 0 (absent). Uranium: 30 ppb. Radium 226+228: 5 pCi/L. Fluoride: 4 mg/L. Barium: 2 mg/L.

MCLGs vs MCLs

Maximum Contaminant Level Goals (MCLGs) represent the level at which no health effects are expected. MCLGs are often lower than MCLs because MCLs factor in treatment feasibility and cost. For contaminants like lead and arsenic, the MCLG is zero.

Secondary Standards

Secondary MCLs cover aesthetic issues (taste, odor, color) rather than health. These include: iron (0.3 mg/L), manganese (0.05 mg/L), pH (6.5-8.5), TDS (500 mg/L). Exceeding these levels is unpleasant but not dangerous.