Water: A Precious Resource Class 7 Science Notes - Chapter 16

Water: Introduction

  • Water is a colourless liquid which constitutes the major part of the earth for survival.
  • 71% of the earth consists of water, hence earth is also called as blue planet.

Origin of water

  • The origin of water is found out to be from a type of meteorite.
  • The major sources of water for human use are lakes, rivers, ponds etc.
  • The chemical composition of water in earth is same as that of some meteorites.

Water Availability

Freshwater and saltwater

  • Freshwater is the pure and naturally occurring water on earth’s surface in rivers, lakes and underground as groundwater.
  • Saltwater is also called as saline water which consists of some amounts of dissolved salts in it. Salt water is present in oceans, seas.

Statistics of availability of water

1. 71 % of Earth consists of water< 2. Out of this 71 %, 97% water is in oceans and seas, remaining 3 % is the freshwater in forms of lakes, rivers. 3. Out of this 3 % of freshwater, 30% is groundwater(not easily accessible), 69% are in the form glaciers, icebergs.( not accessible), out of the remaining 1% of water only 0.006% is used by the people for their uses.

Water Cycle

Physical properties of water

Physical properties of water:

  • Water is a colourless, odourless liquid.
  • Water can change its physical state. Eg: Liquid to solid state and vice versa, Liquid to gaseous state and vice versa.

 

Water cycle

The water cycle is the overall process in which water circulates and is maintained for years to use.

The various processes involved in the water cycle are:

  • Evaporation
  • Condensation
  • Precipitation
  • Transpiration

Evaporation/Transpiration

  • Evaporation is the process in which liquid phase is changed to a gaseous phase.
  • Transpiration is the process by which water evaporates from the surface of leaves through tiny pores called stomata.

Condensation

The process of changing the physical state from gaseous to liquid phase is called as condensation.

Precipitation

Precipitation occurs as a result of the condensation of water vapour in the atmosphere causing water droplets to become heavy and fall down in the form of rain, snow, hail etc.

Ground Water

Ground water

Groundwater is the water present underground or beneath the Earth’s surface in soil spaces and rock formations.

1. Water table – The water table is the upper surface of the ground filled with water.
2. Infiltration – The process of seeping of water from the surface of soil into the ground is called infiltration.
3. Aquifer – The places in which groundwater is stored between the layers of rock below the water table.

Effect of water scarcity on plants

  • Plants need water to grow by absorbing nutrients from the soil.
  • If they do not get enough water, it affects their health and growth eventually killing the plant.

Water Management

Water management

Water management is the effective planning, distribution and use of water resources.

Some types of water management are as follows:

  • Rainwater harvesting or water harvesting: The process of collecting rainwater which recharges the groundwater is called as rainwater harvesting or water harvesting.
  • Drip irrigation: Drip irrigation is the process of watering the crops directly to the roots of the plants using narrow pipes.
  • Bawris: A traditional way of rainwater storage and recharge.​​​​​​​

Introduction to Water: A Precious Resource

Water: Introduction

  • Water is a colourless liquid which constitutes the major part of the earth for survival.
  • 71% of the earth consists of water, hence earth is also called as blue planet.

Origin of Water

  • The origin of water is found out to be from a type of meteorite.
  • The major sources of water for human use are lakes, rivers, ponds etc.
  • The chemical composition of water in earth is same as that of some meteorites.

Leave a Comment

Your email address will not be published. Required fields are marked *