Water Glossary: U-V
| ultraviolet (UV) light | Similar to light produced by the sun; produced by special lamps. As organisms are exposed to UV light, they are damaged or killed. |
| unconfined aquifer | An aquifer that discharges and recharges with an upper surface that is the water table. |
| underground storage tanks | Large tanks buried underground for storing liquids, e.g., gasoline, heating oil; potential source of groundwater contamination if the tank leaks. |
| uranium (U) | A metallic element that is naturally occurring with three main radioactive isotopes (i.e., U-234, U-235, and U-238). Uranium is carcinogenic and can also cause damage to the kidney. Total uranium is regulated by the US Environmental Protection Agency. |
| usable storage capacity | The quantity of groundwater of acceptable quality that can be economically withdrawn from storage. |
| USBR | United States Bureau of Reclamation. |
| virus | (1) A minute organism not visible by light microscopy. A virus is an obligate parasite dependent on nutrients inside cells for its metabolic and reproductive needs. It consists of a strand of either deoxyribonucleic acid or ribonucleic acid, but not both, [inside] a protein covering called a capsid.* |
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*Reprinted from The Drinking Water Dictionary, by permission. Copyright © 2000, American Water Works Association
