Glossary

Learn about the different types of contaminants that might put your family at risk.

absolute
Generally means 100% retention of particulates of the size equal to the filter rating.
absorption
To take up or drink in, as a sponge imbibes water.  The process of assimilation of molecules into the structure of a solid.  One substance taken into the body of another substance. 
acid
A substance which releases hydrogen ions when dissolved in water.  Most acids will dissolve the common metals and will react with a base to form a neutral salt and water. 
acidity
The quantitative capacity of a water or water solution to neutralize an alkali or base.  It is usually measured by titration with a standard solution of sodium hydroxide and expressed in terms of its calcium carbonate equivalent. 
activated carbon (AC)
Adsorptive particles or granules usually obtained by heating carbonaceous material in the absence of air or in steam and possessing a high capacity to selectively remove trace and soluble components from solution. 
activated carbon adsorption
Removal of soluble components from aqueous solution by contact with highly adsorptive granular or powdered carbon.
activated carbon treatment
Treatment process in which water is brought into contact with highly adsorptive granular or powdered carbon to remove soluble components.  Process may be applied to raw water, primary effluent, or chemically clarified wastewater for nonspecific removal of organics, or to secondary effluent as a polishing process to remove specific organics. 
activated silica
A material usually formed from the reaction of a dilute silicate solution with a dilute acid and used as a coagulant aid. 
adsorbent
A material, usually solid, capable of holding gases, liquids, and/or suspended matter at its surface and in exposed pores.  Activated carbon is a common adsorbent used in water treatment. 
adsorption
The process in which matter adheres to the surface of an adsorbent. 
aeration
The process in which air is brought into intimate contact with water, often by spraying water through air, or by bubbling air through water.  Aeration may be used to add oxygen to the water for the oxidation of matter such as iron, or to cause the release of dissolved gases such as carbon dioxide or hydrogen sulfide from the water. 
agglomeration
The coalescence of dispersed suspended matter into larger flocs or particles which settle rapidly. 
air gap
A clear, vertical space between a water or drain line and the flood level of a receptacle used to prevent backflow or siphonage from the receptacle in the event of a negative pressure or vacuum.  Most plumbing codes require the air gap to be a least twice the diameter of the water or drain line with a minimum of 1 ½ inches. 
air stripping
A technique for removal of volatile substances from a solution.  Employs the principles of Henry’s Law to transfer volatile pollutants from a solution of high concentration into an air stream of lower concentration.  The process ordinarily is designed so that the solution containing the volatile pollutant contacts large volumes of air. 
algae
Small primitive plants containing chlorophyll commonly found in surface water.  Excessive growths may create taste and odor problems and consume dissolved oxygen during decay. 
alkali
A group of water soluble mineral compounds usually considered to have moderate strengths as bases as opposed to the caustic or strongly basic hydroxides, although this differentiation is not always made.  In general, the term is applied to the carbonates, borates, phosphates, and silicates when these are present in the water or solution.
alkalinity
The quantitative capacity of a water or water solution to neutralize an acid.  It is usually measured by titration with a standard acid solution of sulfuric acid and expressed in terms of its calcium carbonate equivalent. 
alum
A common name for aluminum sulfate (Al2(SO4)3, used as a coagulant. 
amoeba
A small, single-celled animal or protozoan.
anion
A negatively charged ion in solution such as bicarbonate, chloride, or sulfate.
anode
The positive pole of an electrolytic system; the metal which goes into solution in a galvanic cell.  Anodes of metals such as magnesium or zinc are sometimes installed in water heaters or other tanks to deliberately establish galvanic cells to control corrosion of the tank through the sacrifice of the anode.
aquifer
A layer or zone below the surface of the earth which is capable of yielding a significant volume of water. 
atom
The smallest particle of an element that can exist either alone or in combination with similar particles of the same element or of a different element. 
attrition
The process in which solids are worn down or ground down by friction often between particles of the same material.  Filter media are subject to attrition during backwashing, regeneration, and service.