"Milligrams per liter" means a unit of the concentration of water or wastewater constituent. It is 0.001 g of the constituent in 1,000 ml of water. It has replaced the unit formerly used commonly, parts per million, to which it is approximately equivalent, in reporting the results of water and wastewater analysis. (Ord. 1979-6 § 1 (1.07) (part), 1979)