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HYDROSPHERE (Three quarters of the surface of planet Earth is covered by…

- - - - Water is considered a gas in the form of water vapour. Most water vapour exists in the Earth’s atmosphere as evaporation from surface water. However, it can also come from inside the earth in areas of volcanic activity.
    - - Most liquid water is seawater, found in oceans and seas. A small percentage is inland water, which is made up of both surface water (lakes and rivers) and groundwater (underground water layers, known as aquifers)
        
        Water exists in a liquid state between 0 °C and 100 °C.
        
        salt level:
        Fresh water: very low salt content (inland water)
        Brackish water: moderate salt content (inland water)
        Salt water: high salt content (seawater)
- - - - Build sewage treatment plants to clean domestic waste.Control the emission of toxic substances from industry, and reduce thermal pollution by using cooling ponds and cooling towers.Practice crop rotation and reduce the use of chemical pesticides and fertilizers in agriculture.
- - - - A river is a flowing body of fresh water. Rivers flow into the sea, or into other lakes or rivers and form V-shaped valleys. Rivers are a vital source of water for human beings. They are also used for traditional inland transportation on boats.
      - In rivers that flow into calm sea, a delta can form. There is no sea current to remove river sediment, so it is able to build up in a triangular shape at the river mouth.
      - A lagoon is a shallow lake that forms on coastlines. Lagoons have at least one inlet from the sea.
      - A lake is a body of fresh, brackish or salt water. The water in lakes comes from rivers, groundwater or from melted glaciers. Lakes are entirely surrounded by land and are different sizes.
      - In rivers that flow into the sea, a wide estuary of brackish water can form from sea currents that transport river sediment. Estuaries and nearby coastal areas are often heavily populated by humans .
      - A marsh is a type of wetland found at the edge of other bodies of water, such as rivers, lakes and the sea. They can be formed of fresh, salt or brackish water and often flood .
      - Water accumulates from rain and groundwater in low-lying areas to form wetlands. Wetlands are often seasonal: a shallow layer of water covers the ground for only part of the year.
    - - Groundwater is water that is stored underground, beneath the surface of the Earth.
    - - Glaciers are large masses of slow-moving ice.
        
        Glaciers can only exist in areas of the Earth where the temperature is always, or nearly always, below 0°C
        
        Glaciersmove downhill very slowly and this is because of their immense weight and the gravity of the Earth. Their movement erodes the original landscape and forms U-shaped valleys.
        
        As they move, glaciers transport moraines. This rocky debris can be seen in sheets and piles where the glacier has passed or on the surface of the ice.
- - - - Collection: the water is collected at source from reservoirs, lakes, rivers and aquifers.
        
        Purification: to make water safe to drink it is processed at water treatment facilities. This treatment turns natural water into drinking water and achieves a uniform taste, colour and smell.
        
        Wastewater treatment: After the water has been used it needs to be cleaned before returning to the environment. Treatment processes can be natural or artificial
        :Natural: water is cleaned through soil, vegetation or by natural organisms.
        Artificial: water is cleaned in wastewater treatment facilities or is treated by lagooning. This process involves moving water through a series of ponds where air is added to it. This makes the sediment float to the bottom of the pond where it is cleaned by anaerobic and aerobic bacteria.