- Water is a colorless and odorless substance found all over Earth.
- Each molecule is made of one oxygen and two hydrogen atoms held together by strong c bonds.
- Water is found in three different forms on Earth – gas, solid, and liquid.
- The form water takes depends on the temperature. Water on our planet flows as liquid in rivers, streams, and oceans; is solid as ice at the North and South Poles; and is gas (vapor) in the atmosphere.
- Water is also underground and inside plants and animals. All living things need water in some form to survive on Earth.
- People can go weeks without food, but can live only a few days without water.
Properties of water
- Each molecule of water consists of one atom of oxygen and two atoms of hydrogen, so it has the chemical formmula H2O.
- The arrangement of atoms in a water molecule,explains many of water’s chemical properties. In each water molecule, the nucleus of the oxygen atom attracts electrons much more strongly than do the hydrogen nuclei with only one positively charged proton.
- This results in a negative electrical charge near the oxygen atom (due to the "pull" of the negatively charged electrons toward the oxygen nucleus) and a positive electrical charge near the hydrogen atoms. A difference in electrical charge between different parts of a molecule is called polarity.
- polar molecule is a molecule in which part of the molecule is positively charged and part of the molecule is negatively charged.
Sources of water
There are 2 main sources of water
- Ground water-it occurs below the surface of Earth.It is also called subsurface water to distinguish it from surface water, which is found in large bodies like the oceans or lakes or which flows overland in streams. A vast amount of groundwater is distributed throughout the world, and a large number of groundwater reservoirs are still underdeveloped or not been investegated . Scientists estimate that some 5.97 gallons (22.6 million cubic km 5.8 million cubic miles) of groundwater reside in the upper 3 km (1.6 miles) of Earth’s surface. The most frequently investigated or exploited groundwater reservoirs are of the unconsolidated . (mainly sand and gravel) or carbonate hardrock type found in alluvial valleys and coastal plains under temperate or arid conditions.Though some groundwater dissolves substances from rocks and may contain traces of old seawater, most groundwater is free of pathogenic organisms, and purification for domestic or industrial use is not necessary.
- Surface water-Most surface water comes from rainfall
(precipitation) runoff from the surrounding land
area (catchment). Of course not all runoff ends up in
rivers, some evaporates, some is used by vegetation
and part of it soaks into the ground recharging our
groundwater systems, some of which can then seep
back into the riverbeds.
At a certain depth below the land surface, called
the water table the ground becomes saturated with
water. If a river happens to cut into this saturated
layer, then water will seep out of the ground into the
river. Groundwater seepage is most commonly seen
in the form of springs eg. Berry Springs, Katherine
Hot Springs and Bitter Springs.
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