Class 7|Water | Science | CBSE and KSEEB | Vista's Learning |Reema Sarkar

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Chapter -16 Water-A precious Resource
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Water

1. It is the most vital natural resources
2. Sources of water are river, lakes, pond etc.
3. It is found in all three states i.e. solid,
   liquid and gas

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Importance of water

• Water carries nutrients to all cells in our body
  and oxygen to our brain.
• Water allows the body to absorb and assimilate
  minerals, vitamins, amino acids, glucose, and
  other substances.
• Water flushes out toxins and waste.
• Water helps to regulate body temperature

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Percentage of water available on Earth

• About 71 of the earths surface is covered with
  water.
• Almost all the water on the earth is contained
  in the seas and oceans, rivers, lakes, ice caps,
  as groundwater and in the atmosphere.
• Most of this water is not fit for human
  consumption directly.
• The water that is fresh for use is freshwater

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Forms of water

• Solid
• Liquid
• Gas

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Water Cycle

• The water cycle shows the continuous movement of
  water within the Earth and atmosphere.
• It is a complex system that includes many
  different processes.
• Liquid water evaporates into water vapor,
  condenses to form clouds, and precipitates back
  to earth in the form of rain and snow

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Process of Water Cycle
Source NCERT
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Important sources of water

• The important sources of water are
• Groundwater
• Surface water and
• Rain water

Source NCERT
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Groundwater as important source of water

• Groundwater is water that has infiltrated the
  ground to fill the spaces between sediments and
  cracks in rock.
• 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.

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Groundwater
Aquifer
Water Table
Infiltration
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Infiltration

• The rainwater and water from other sources such
  as rivers and ponds seeps 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.

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Water Table

• The upper level 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.

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Aquifer

• At places the groundwater is stored between
  layers of hard rock below the water table.
• This is known as an aquifer.
• Water in the aquifers can be usually pumped out
  with the help of tube wells or hand pumps.

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Groundwater and water table
Source NCERT
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Depletion of watertable
Increasing Irrigation Requirement
Increasing population
Increasing Industries
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Distribution of water

• The distribution of water over the globe is quite
  uneven due to a number of factors.
• Some places have good amount of rain and are
  water-rich. On the other hand, there are deserts
  which have scanty rainfall. India is a vast
  country and the rainfall is not the same
  everywhere.
• Some regions have excessive rains while some
  others have very little rainfall. Excessive rains
  cause floods, whereas the absence of rains
  results in droughts. Therefore, some regions in
  our country may have floods while others may
  suffer from droughts at the same time.

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Water Management

• Leaking taps is another source of huge water
  wastage. Prevent leakage of water
• The rainwater can be used to recharge the
  groundwater. This is referred to as water
  harvesting or rain water harvesting
• At many places in India an age old practice of
  water storage and water recharge like the
  bawris. Bawri was the traditional way of
  collecting water.
• A farmer using water in the field can also use
  water economically. Drip irrigation is a
  technique of watering plants by making use of
  narrow tubings which deliver water directly at
  the base of the plant.

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Source NCERT
Drip Irrigation
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Effect of water scarcity on Plants

• The plants need water to get nutrients from the
  soil to prepare their food.
• The green character of the planet shall be lost.
  This may mean the end of all life, for a world
  without plants shall mean no food, no oxygen,
  not enough rain, and innumerable other problems.

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