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

According to the CBSE Syllabus 2023-24, this chapter has been removed from NCERT Class 7 Science textbook.

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 the Earth is also called a blue planet.

Origin of water

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

To know more about Water, visit here.

Water Availability

Freshwater and Saltwater

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

Statistics of Availability of Water

1. 71 % of Earth consists of water<

2. Out of this 71 %, 97% of water is in oceans and seas, and the remaining 3 % is freshwater in the form of lakes and rivers.

3. Out of this 3 % of freshwater, 30% is groundwater(not easily accessible), and 69% is in the form of glaciers and 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. For example, Liquid to solid state and vice versa, Liquid to gaseous state and vice versa.

For more information on Water Cycle, watch the below video

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 the 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 condensation.

For more information on Types of Condensation, watch the below video

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.

To know more about Water Cycle, visit here.

Groundwater

Groundwater

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 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.

To know more about Ground Water, visit here.

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.​​​​​​​

To know more about Water Management, visit here.

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 a blue planet.

Origin of Water

• The origin of the water is found 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 on the Earth is the same as that of some meteorites.