Why are MCLs and ALs reported in parts per million and parts per billion?

Answer 1

Maximum Contaminant Levels (MCLs) and Action Levels (ALs) are reported in parts per million (ppm) and parts per billion (ppb) to provide precise measurements of contaminants in water and ensure public health safety. These units allow for the detection of very low concentrations of harmful substances, which is critical since even trace amounts can pose significant health risks. Using these standardized units facilitates comparison and compliance with regulatory limits set by health and environmental agencies.