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

A circular movement whirlpool occurring in flowing water caused by currents set up in the water by obstructions. 
A device utilizing a nozzle and throat and installed in a stream of water to create a partial vacuum to draw air or liquid into the stream.  Commonly used to draw brine into a water line for the regeneration of an ion exchange water softener.
effective size
A measure of the size of particles of ion exchanger or filter media, defined as the diameter of a specific particle in a bed, batch, or lot which has 10 percent smaller and 90 percent larger particles.
The stream emerging from a system or process such as the softened water from an ion exchange softener.  The filtrate water from a filter.
(See eductor.)
A fundamental particle found in the atom and which carries a single negative charge.  In a neutral atom, the positive charges of the nucleus are balanced by an equal number of negative electrons in the field surrounding the nucleus.  Ions are formed when atoms gain or lose electrons, thus achieving positive or negative net charges. 
The disposable filtering cartridge itself in a replaceable cartridge-type filter.
The point at which a process is stopped because a predetermined value of a measurable variable is reached; the endpoint of an ion exchanger water softener service run is the point at which the hardness of the softener effluent increases to a predefined concentration, often 1.0 grain per gallon; the endpoint of a filter service run may be the point at which the pressure drop across the filter reaches a predetermined value; the endpoint of a titration is the point at which the titrant produces a predetermined color change, pH value, or other measurable characteristic.
The abbreviation for “equivalent per million.”
The state in which the action of multiple forces produces a steady balance or seeming lack of change; may be due to a true stop in action or due to continuing actions which neutralize each other resulting in no net change.
equilibrium reaction
A chemical reaction which proceeds primarily in one direction until the concentrations of reactants and products reach an equilibrium which usually can be expressed as ratio or other mathematical relationship.
equivalent per million
A unit of concentration used in chemical calculations, calculated by dividing the concentration in ppm or mg/L by the equivalent weight.
equivalent weight
The weight in grams of an element, compound, or ion which would react with or replace 1 gram of hydrogen; the molecular weight in grams divided by the valence.