U |
| Unaccounted for water | Unaccounted for water (UFW) is water that has been produced and is “lost” before it reaches the customer. Losses can be real losses (through leaks, sometimes also referred to as physical losses) or apparent losses (for example through theft or metering inaccuracies). High levels of UFW are detrimental to the financial viability of water utilities, as well to the quality of water itself. UFW is typically measured as the volume of water "lost" as a share of net water produced. |
| Unconfined Aquifer | Aquifer containing unconfined groundwater, that is having a water table and an unsaturated zone. |
| Unconsolidated | A term used to refer to sediments that are not cemented together. |
| Unsupervised Classification | Categorization of digital image data by computer processing based solely on the image statistics without availability of training samples or prior knowledge of the area. The classification creates natural groupings in the image values, called spectral clusters or classes. In this fashion, values with similar grey levels are assumed to belong to the same cover type. The analyst must then determine the identity of these spectral clusters. |
| Unsustainable | Unable to continue indefinitely. |
| Upper basin states | Countries located upstream of an international river basin. |
| Upper Kunene | The upper portion of the Kunene catchment, the portion of the river closest to the source. |
| Upper waters of a river | The upper portion of the river, closest to the source. |
| Upstream | In the direction towards the source of a stream. |
| Upstream Tributary | River, brook or stream that flows into another stream, above the location to which you are referring to. |
| Urban | An area with an increased density of human-created structures in comparison to the areas surrounding it |
| Urban heat island | Refers to the increased temperature in urban areas relative to surrounding rural areas. |
| Urbanization | The expansion of a city or metropolitan area, often due to population growth caused by the movement of people from rural to urban areas. |
