Concentration is the amount of a substance in solution. It is usually expressed as milligrams per liter (mg/l), parts per million (ppm). PPM is usually the same as mg/l if water is the solvent. It can also be noted as grains per gallon, gpg. Test procedures are now capable of detecting water in parts per billion, ppb, or micrograms per liter.
Abbreviated as \(C\)