Glossary

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

ultrafiltration (UF)
The process of removing colloidal and dispersed particles from a liquid by passing the liquid through a membrane under high pressure.  Separation or removal of particulates of more than 10Ǻ and less than 200 angstroms.
ultraviolet radiation (UV)
Light waves shorter than visible blue-violet waves of the spectrum having wave lengths of less than 3,900 D Angstroms.
ultraviolet ray
Light rays beyond the violet of the spectrum invisible to humans.
underdrain
A drain that carries away groundwater or the drainage from prepared beds to which water or wastewater has been applied. 
uniform flow
A flow in which the velocities are the same in both magnitude and direction from point to point along the conduit.
uniformity coefficient
The degree of variation in the size of the grains that constitute a granular material; the ration of (a) the diameter of a grain of a size that is barely too large to pass through a sieve that allows 60 percent of the material (by weight) to pass through, to (b) the diameter of a grain of a size that is barely too large to pass through a sieve that allows 10 percent of the material (by weight) to pass through.  The coefficient is unity for any material having grains all the same size, and it increases above unity with variation in size of grain.
upflow
A term used to indicate the direction (up) in which water or regenerant flows through an ion exchanger or filter media bed during any phase of the operating cycle.  Also referred to as counter-current flow.