Water : Glossary

There are 59 documents in this section.

  • Water quality

    24 January 2001

    The definition of water quality will vary to some extent depending upon the proposed use. Water intended for irrigation or for certain industrial purposes will not have to meet the same quality standards as water intended for drinking, for example. However, there are certain factors that determine water quality whatever the use. They can be classified as physical properties, chemical properties and biological properties.

  • Water quality standards

    24 January 2001

    Acceptable standards for water quality have been developed at both the national and international level. The World Health Organisation (WHO) has published guidelines for drinking-water quality, for example, and the European Commission has produced a directive which applies to the quality of water intended for human consumption. Elsewhere all developed nations have established standards for water quality, and some progress has been made among the developing nations. Published standards typically include maximum allowable concentrations (MACs) of specific toxic elements - for example, heavy metals - and guide levels (GL) for those considered less harmful - for example, acidity or calcium (Ca).

  • Watershed

    24 January 2001

    A watershed is an area of land that is drained by a river system and its tributaries. Watersheds can be visualised as physical basins, the "rims" of which are ridges of high land that separate adjacent watersheds.

  • Algal bloom

    23 January 2001

    Abnormally increased biomass of algae in a lake or river. Algal blooms occur naturally in spring and early summer, when the rate of reproduction of the algae outstrips that of their consumers. However, the most serious algal blooms are associated with human activities. Phosphates and nitrates carried into waterways in sewage, agricultural fertilisers and detergents, provide the nutrients that cause explosive growth in the algae population.

  • Arsenic

    23 January 2001

    A highly toxic element which exists in three forms - grey, black and yellow arsenic. It occurs naturally in the environment, being released from arsenic-bearing rocks through weathering. Arsenic accumulates in the environment so that small doses, relatively harmless individually, may eventually kill organisms - including people.

  • Eutrophication

    23 January 2001

    The occurrence of high nutrient levels in freshwater and marine ecosystems, usually resulting in excessive plant growth and the death of animal and some plant life due to oxygen deprivation.

  • Groundwater

    23 January 2001

    The water that accumulates in the pore spaces and cracks in rocks beneath the earth's surface. It originates as precipitation and percolates down into sub-surface aquifers. The upper limit of groundwater saturation is the water table. Groundwater moves under the influence of gravity, although usually only slowly, and may return to the surface naturally - for example, through springs. Increasingly, it is pumped from wells and boreholes for human use. The rate of withdrawal commonly exceeds the rate the rate of recharge, and in many areas the groundwater supply is simply declining.

  • Irrigation

    23 January 2001

    The provision of water for crops in areas where the natural precipitation is inadequate for crop growth. The water may be obtained from natural or artificial surface storage systems (such as lakes or reservoirs) or from the groundwater system. Irrigation takes many forms from the total flooding associated with paddy-rice production to various sprinkler systems that attempt to emulate precipitation.

  • Aridity

    23 January 2001

    Permanent dryness caused by low average rainfall, often (but not always) in combination with high temperatures. The deserts of the world are permanently arid, with rainfall amounts of less than 100 mm per year, and evapotranspiration rates well in excess of that amount.

  • Catchment

    23 January 2001

    A drainage basin, or the area drained by a particular river system. Adjacent drainage basins are separated by watersheds. In North America, the term watershed refers to the entire drainage basin, and the height of land between basins referred to as a divide.