Glossary of Terms - M
A B C D E F G H I J K L M N O P Q R S T U V W Z
magnesium (Mg) - One of the elements in 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 which identify hard water.
manganese (Mn) - An element sometimes found dissolved in ground water, usually with - but in lower concentrations than - iron. Manganese causes black stains and other problems similar to iron. It can be removed by a water softener.
manganese greensand - Greensand which has been processed to incorporate the higher oxides of manganese into its pores and on its surface. 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 (see greensand, manganese zeolite).
manganese zeolite - Synthetic gel zeolite which has been processed in the same manner as manganese greensand, and used for similar purposes.
maximum contaminant level (MCL) - The maximum allowable concentration of a contaminant in water as established in the U.S. EPA Drinking Water Regulations.
MCL - Maximum Contaminant Level
mechanical filter - A pressure or gravity filter designed to physically separate and remove suspended solids from a liquid by mechanical (physical) means rather than by chemical means.
media - The plural form of "medium".
medium - See filter media.
Methyl Tertiary-Butyl Ether (MTBE) - A gas additive that was incorporated in the mid-80’s into gasoline to reduce carbon monoxide (CO) emissions. It has increasingly appeared in groundwater due to spills of reformulated gasoline and leaking underground storage tanks at gasoline stations. It is highly soluble and its appearance typically marks the leading front of a contamination plume. MTBE is adsorbed onto activated carbon.
mg/L - milligrams per liter.
micrometer - Formally known as micron. A linear measure equal to one millionth of a meter or .00003937 inch. The symbol for the micrometer is "µm".
micron - See micrometer.
micron rating - The term applied to a filter medium to indicate the particle size above which all suspended solids will be removed throughout the rated capacity. As used in the water treatment industry standards, this is may be an "absolute rating or a "nominal rating”.
mil - One thousandth of an inch.
milli - The prefix used with units of measure to indicate one thousandth of the unit. Example: a milliliter is one thousandth of a liter.
milligram per liter (mg/L) - A measure of concentration of a dissolved substance. A concentration of one mg/L means that one milligram of a substance is dissolved in each liter of water. For practical purposes, this unit is equal to parts per million (ppm) since one liter of water is equal to one million milligrams.
millimicron - A unit of length equal to 10-3 microns correctly called a nanometer (nm).
mineral - A term applied to inorganic substances such as rocks and similar matter found in the earth 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 the inorganic ions found in water. The term has been applied to ion exchangers, stemming from the early use of natural zeolite. The term is inappropriate to the modern organic ion exchange resins.
mineral acidity - Acidity due to the presence of strong inorganic acids such hydrochloric, sulfuric and nitric acids, as opposed to weak acidity due to carbonic acid or acetic acid.
mole - The molecular weight of a substance, usually expressed in grams.
molecule - The smallest particle of a substance which will still retain the essential composition and properties of that substance.
most probable number (MPN) - The term used to indicate the number of microorganisms which, according to statistical theory, would be most likely to produce the results observed in certain bacteriological tests; usually expressed as a number per 100 ml of water.
MPN - See most probable number.
MTBE - See Methyl Tertiary-Butyl Ether
mushing - Mushing of water softener salt occurs when salt pellets break down into their crystallized form. See bridging.