The outlet fitting at the bottom of a swimming pool through which water passes to the recirculating pump (often erroneously referred to as the “main drain”.
MAKE-UP WATER
Fresh water used to fill or refill the pool, spa or hot tub.
MEMBRANES
Thin films constructed of cellulosic or synthetic materials, which are designed to provide selective transport of solutes. Widely used for hemodialysis, micro filtration, ultrafiltration and reverse osmosis, membranes may be either homogeneous or asymmetric. Homogeneous membranes have a uniform structure or cross-section while asymmetric membranes have a dense "skin" which overlays a porous substructure.
METHEMOGLOBINEMIA
The presence in blood of methemoglobin, a substance related to normal oxyhemoglobin, but having no oxygen-carrying capabilities and induced by exposure of blood to certain toxic chemicals, such as nitrites.
Mg/l
Milligrams per liter. A measure of concentration of a dissolved substance in a liquid. 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 in weight to one million milligrams. Thus, a liter of water containing 10 milligrams of calcium has 10 parts of calcium per one million parts of water or 10 parts per million (10 ppm).
MICRO FILTRATION
The separation or removal from a liquid of particulates and micro-organisms in the size range of 0.1 to 2 microns in diameter.
MICRO POROUS
In the context of water purification, membranes having an average pore size, which is between 0.1 and 1.0 micron in diameter.
MICROFARAD
A measurement of capacitance (electrical storage capability). Capacitors or condensers have a range listed on the casing (15-22 MFD, example) showing the capacity it can handle. They will also show the maximum voltage they can handle (370V, example).
MICROHM
One millionth of an ohm. The unit of measurement for testing the electrical resistance of water to determine its purity. The closer water comes to absolute purity, the greater its resistance to conduction of an electrical current. Absolute pure water has a specific resistance over 18 million ohms (megohms) across one centimeter of water at a temperature of 78 degrees Fahrenheit.
MICRON
A unit of linear measure. It is one millionth of a meter, or one thousandth of a millimeter. The smallest particle than can be distinguished by the naked eye would be about 40 microns across.
MICRON RATING
A measurement applied to filters or filter media to indicate the particle size at which a substantial percentage of suspended solids above that size will be removed. As used in the water treatment industry standards, this may be an absolute rating or a nominal rating.
MICRONS
A measurement used in filtration. A millionth part of a specified substance.
MICROWATT-SECONDS PER SQUARE CENTIMETER
A unit of measurement of intensity and retention, or contact time in the operation of ultraviolet (U/V) systems.
MILLILITERS/MINUTE
A common measurement for the flow rate of small RO systems. Usually measured with a graduate cylinder. One thousandth of a liter per minute. Milliliters/min x.38 = gal/day.
MIXED BED
The intermixing of two or more filter or ion exchange products in the same vessel during a service run. The most common use is in ion exchange systems having a 40/60 percent cation to anion resin bed such as that for a deionization polisher system. In filtration, there may be an intermixing of two or more media in a single tank with each stratified into separate layers.
MOD MEDIA
Short for Modular Media, a type of filtration system. Consists of filters within filters - interchangeable and replaceable.
MODEL NUMBER
Identification nomenclature for a product.
MONOVALENT ION
A cation or anion having a single electrical charge.
MSDS
Material Safety Data Sheet - Required by law for products with potential for pollution or health risks(examples = paint, petroleum products).
MTBE:(Methyl Tertiary Butyl Ether)
A volatile organic chemical (VOC) used as an octane-enhancing lead substitute and more recently as an oxygenating agent in gasoline to reduce carbon monoxide emissions from automobiles. MTBE is volatile, flammable and highly soluble in water. During refueling and gasoline production, MTBE is volatilized to the atmosphere where it dissolves into the atmospheric moisture and returns to earth as precipitation, polluting our water supplies. Since MTBE does not adsorb well with organic matter in soils it is easily washed away. In surface water, MTBE volatilizes into the air. While in ground water, MTBE persists and moves freely. MTBE occurrences in ground water above 40 ppb have so far been attributed to point source contamination such as underground gasoline tank leaks, overflows, etc. EPA has tentatively classified MTBE as a potential human carcinogen.
MULTIPLE FILTER CONTROL VALVE
A multi-port valve with at least four positions for varous filter operations, which combines in one unit the function of two or more single direct flow valves (Dial Selector Valve).
MURIATIC ACID
A commercial name for hydrochloric acid. Used for lowering the pH and alkalinity of pool water.