What does the unit "mg/L" measure in water?

The unit "mg/L" measures mass concentration, indicating how many milligrams of a specific substance are present in one liter of water. This measurement is widely used in water quality testing and environmental monitoring to quantify the concentration of various pollutants, nutrients, or chemicals in water samples.

Understanding mass concentration is crucial for assessing water safety and compliance with environmental regulations. For instance, when measuring contaminants in drinking water or assessing the pollution levels in a river, knowing the mass concentration helps determine whether the water meets health and environmental standards.

On the other hand, volume concentration would express the concentration relative to the volume of the substance rather than its mass, which is not applicable in this context. Pressure and temperature are units measuring different physical properties entirely and are not relevant to the concentration of a substance in water. Therefore, recognizing that "mg/L" specifically refers to mass concentration is essential for accurate interpretation in water quality assessments.