National Council of Examiners for Engineering and Surveying (NCEES) Fundamentals of Engineering (FE) Environmental Practice Exam

Parts per million (ppm) is commonly used to express the concentration of substances in water. In the context of water measurement, 1 ppm is equivalent to 1 milligram of a substance per liter of water (mg/L). This relationship arises because water has a density close to that of pure water at standard conditions, where 1 liter of water weighs approximately 1,000 grams. Thus, when 1 milligram of a solute is dissolved in 1 liter of water, it results in a concentration of 1 ppm.

Using mg/L for measuring ppm allows for straightforward understanding and communication of water quality and pollutant concentrations, which is critical in environmental analysis and regulatory compliance. This measurement unit is widely accepted in scientific research, environmental studies, and water quality assessments.