Glossary

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

vacuum breaker
A mechanical device which automatically vents a water line to the atmosphere when subjected to a partial vacuum, thus preventing backflow. (See backflow, air gap, backflow preventer).
valence
A small positive or negative whole number, which indicates the net number of electrons gained or lost in the formation of an ion, and thus the numbers of each kind of ion necessary for a balanced chemical reaction.  For example, two hydrogen ions (each with a valence of +1) must be present for each ion of oxygen (-2) to form a molecule of water (H2O).
viable
Alive and capable of continued like.
virus
The smallest form of life known to be capable of producing disease or infection, usually considered to be of large molecular size.  They multiply by assembly of component fragments in living cells, rather than by cell division, as do most bacteria.
viscosity
The resistance of fluids to flow, due to internal forces and friction between molecules.
void volume
The volume of the pores or spaces between particles of ion exchanger, filter media, or other granular material, often expressed as a percentage of the total volume occupied by the material.
volatile
Capable of vaporization at a relatively low temperature.
volatile solids
Matter which remains as a residue after evaporation at 105 or 180 ° C., but which is lost after ignition at 600 ° C.  Includes most forms of organic matter.
volumetric
Referring to measurement by volume rather than weight.