Langelier's index – A calculated number used to predict whether or not a water will precipitate, be in equilibrium with, or dissolved calcium carbonate. It is sometimes erroneously assumed that any water which tends to dissolve calcium carbonate is automatically corrosive.
lime – The common name for calcium oxide (CaO); hydrated lime is calcium hydroxide Ca(OH)2.
lime scale – Hard water seal containing a high percentage of calcium carbonate.
limestone – A sedimentary rock, largely calcium carbonate, and usually also containing significant amounts of magnesium carbonate.
liter – The basic metric unit of volume; 3,785 liters equals 1 U.S. gallon; 1 liter of water weights 1000 grams.
magnesium – On of the elements making up the earth's crust, the compounds of which when dissolved in water make the water hard. The presence of magnesium in water is a factor contributing to the formation of scale and insoluble soap curds.
manganese – An element sometimes found dissolved in ground water, usually with dissolved iron but in lower concentrations; causes black stains, and other problems similar to iron.
manganese greensand – Greensand which has been processed to incorporate in its pores and on its surface the higher oxides of manganese. The product has a mild oxidizing power, and is often used in the oxidation and precipitation of iron, manganese and/or hydrogen sulfide, and their removal from water.
media – The selected materials in a filter that form the barrier to the passage of certain suspended solids or dissolved molecules.
micron – A linear measure equal to one millionth of a meter.
milligram per liter (mg/L) – A unit concentration of matter used in reporting the results of water and waste- water analyses. In dilute water solutions, it is practically equal to the part per million, but varies from the ppm in concentrated solutions such as brine. As most analyses are performed on measured volumes of water, the mg/L is a more accurate expression of the concentration, and is the preferred unit of measure.
mineral – A term applied to inorganic substances, such as rocks and similar matter found in the earth's strata, as opposed to organic substances such as plant and animal matter. Minerals normally have definite chemical composition and crystal structure. The term is also applied to matter derived from minerals, such as a inorganic ions found in water. The term has been incorrectly applied to ion exchangers, even though most of the modern materials are organic ion exchange resins.
molecule – The simplest combination of atoms that will form a specific chemical compound; the smallest particle of a substance which will still retain the essential composition and properties of that substance, and which can be broken down only into atoms and simpler substances.