- Books Name
- CBSE Class 7 Science Book
- Param Publication
- CBSE Class 7
(b) Groundwater as an important source of water
If we dig a hole in the ground near a water body we may find that the soil is moist. The moisture in the soil indicates the presence of water underground. If we dig deeper and deeper, we would reach a level where all the space between particles of soil and gaps between rocks are filled with water . The upper limit of this layer is called the water table. The water table varies from place to place, and it may even change at a given place. The water table may be at a depth of less than a metre or may be several metres below the ground. The water found below the water table is called groundwater.
The rain water and water from other sources such as rivers and ponds seep through the soil and fills the empty spaces and cracks deep below the ground. The process of seeping of water into the ground is called infiltration. The groundwater thus gets recharged by this process. At places the groundwater is stored between layers of hard rock below the water table. This is known as an aquifer.
Spring water : Springs are formed by percolation of rain water into soil. Springs supply water to wells and lakes.
Well Water : The rain water seeps through the soil and goes down and is stored over rocks or hard earth crust. On digging the well this underground water becomes available to us. This is known as well water. This water may not be pure and may contain impurities such as suspended particles, bacteria and other microorganisms.
1.5 Sources of water
The natural sources of water are rain, springs, wells, rivers and seas.
(a) Surface water : It is the water present on the surface of earth. The water present in oceans, seas, rivers, springs, etc. comes under surface water.
(i) Rain water : Rain water is considered to be the purest form of natural water (distilled water) free from impurities.
When the water vapours go high up in the air they condense to form clouds. The water drops come down as rain.
(ii) River water : Rivers are formed by melting of snow on the mountain, and also sometimes from the rain water. River water is also not a pure source.
(iii) Sea water : Sea water is the largest natural source of water. However, it is also the source of common salt and other important chemicals. It is the most impure form of water. All the impurities dissolved in river water are carried into the sea. Sea water cannot be used for drinking purpose because of high salinity and impurities.