Water : Glossary

There are 59 documents in this section.

  • Percolation

    24 January 2001

    Vertical movement of water downwards through soil or rock in the unsaturated zone immediately beneath the surface.

  • Precipitation

    24 January 2001

    Any solid or liquid water particles falling to the earths' surface from the atmosphere. It includes rain, snow, hail and sleet, but 'precipitation' and 'rain' are often treated as synonyms.

  • Rain

    24 January 2001

    Precipitation in the form of liquid water droplets. Droplets vary in size but exceed 0.5mm in diameter. Smaller droplets are considered to be drizzle.

  • Sahel

    24 January 2001

    A semi-arid to arid area, subject to seasonal and long-term drought, in West Africa south of the Sahara Desert. Named from the Arabic word 'border', since it borders the desert, the Sahel proper consists of six nations - Senegal, Mauretania, Mali, Burkina Faso, Niger and Chad - but the name has come to include adjacent nations that suffer from problems of drought, famine and desertification that are characteristic of the Sahel.

  • Salinisation

    24 January 2001

    The build-up of salts in soil as a result of the capillary flow of saline water towards the surface. Salinisation is a common problem in areas where agriculture requires irrigation. There, the natural process is exacerbated by the evaporation of irrigation water that not only adds salts directly to the soil, but also encourages sub-surface water to be drawn from deeper levels to the surface where it is evaporated. At best, it can lead to a reduction in crop yields; at worst, it made the land sterile and unsuitable for agriculture.

  • Schistosomiasis

    24 January 2001

    A tropical or subtropical intestinal disease of humans caused by parasitic flatworms or flukes. Using snails as intermediate hosts, the flukes are spread from person to person through polluted water and insanitary living habits. Deteriorating health and reduced resistance usually cause those infected to die of secondary diseases rather than schistosomiasis itself. Schistosomiasis is prevalent in Africa, South America and tropical Asia, where as many as 200 million people are infected.

  • Water

    24 January 2001

    Pure water is a colourless, odourless liquid that is a compound of hydrogen and oxygen (H20). Natural water in the environment is never pure, but contains a variety of dissolved substances. Sea water, for example, is a solution of sodium chloride (NaCl - common salt) and other salts; rainwater can be acidic because of the carbon dioxide (CO2) that it contains and the water in rivers may include minerals dissolved from the rocks over and through which it has flowed. Water can exist as a solid (ice), liquid (water), or gas (water vapour) and changes readily from one to the other, either releasing or taking up energy as it does so.Some 97 per cent of the world's water is in the oceans, while a further 2 per cent is in the form of ice and snow, which leaves only 1 per cent available as freshwater for plants and animals. Survival on such small amount is made possible by the natural recycling of the water in the hydrological cycle, which not only replaces the water once is has been used, but also cleans it.

  • Wetlands

    24 January 2001

    Swamps, marshes, fens, tidal marshes, peatlands and other ecosystems which are dominated by water. The presence of water may be permanent, temporary or seasonal and it may by fresh or salt, but the plant and animal organisms in wetlands have adapted to that situation to create unique communities that reflect the conditions at a specific site. Wetlands provide habitat for fish and wildlife, act as staging areas for migrating wildfowl, filter sediments and control flooding in stream systems and protect the shore from erosion in coastal areas.

  • Water vapour

    24 January 2001

    Water in its gaseous state, produced from liquid water by evaporation or by respiration from animals and transpiration from plants. Its presence in the atmosphere contributes to humidity and through subsequent condensation to precipitation. Water vapour is also a greenhouse gas.

  • Water table

    24 January 2001

    The upper level of the saturated or groundwater zone in the rocks beneath the earth's surface. In the general, the shape of the water table follows that of the surface, but in places it may reach the surface, creating ponds or natural springs. The depth of the water table in any one area varies with such factors as input from precipitation, loss through sub-surface flow and pumping of groundwater from wells.