About three-fourths of Earth’s surface is covered with water.
Most of this water is salty seawater.
Only a small amount is freshwater that people can use.
Usable freshwater mainly comes from:
Rivers and lakes
Rainfall
Surface runoff
Groundwater
The hydrological cycle is the continuous movement of water between the Earth’s surface and the atmosphere.
The main steps are:
The Sun heats water in oceans, rivers, lakes, and soil.
Water changes into vapour through evaporation.
Plants also release water vapour through transpiration.
Water vapour rises and cools.
It changes into tiny water droplets and forms clouds through condensation.
Water falls back to Earth as precipitation, such as rain or snow.
Some water flows over the ground as surface runoff.
Some water enters the soil and becomes groundwater.
Water eventually returns to rivers, lakes, and oceans.
Because water is continuously renewed through this cycle, it is called a renewable resource.
Freshwater contains very little salt and can be used by people, animals, and plants.
Important sources of freshwater include:
Rain
Rivers
Lakes
Ponds
Glaciers
Groundwater
Freshwater is needed for drinking, cooking, washing, agriculture, industries, and producing electricity.
Surface runoff is water that flows over the land after rain or melting snow.
It may:
Flow into streams and rivers
Fill lakes and ponds
Carry soil and pollutants
Eventually reach the sea
The amount of runoff depends on rainfall, the slope of the land, soil type, vegetation, and how much water the ground can absorb.
Groundwater is water stored below the Earth’s surface.
It is found in spaces between soil particles and cracks in rocks. Rainwater slowly enters the ground and recharges underground water supplies.
People obtain groundwater through:
Wells
Hand pumps
Tube wells
Borewells
Groundwater is useful, but excessive pumping can lower the water table and cause wells to dry up.
Water scarcity means that there is not enough safe and usable water for people’s needs.
Water scarcity can occur because of:
Low rainfall
Drought
Unequal distribution of water
Rapid population growth
Excessive use of groundwater
Intensive farming
Industrial use
Urbanisation
Water pollution
Poor water management
A place does not have to be completely dry to suffer from water scarcity. It may have water, but the water could be polluted, badly distributed, or used faster than it is replaced.
Water is not equally available everywhere.
Some areas receive heavy rainfall, while others receive very little. Rainfall can also vary during the year.
For example:
A place may receive heavy rain during the monsoon.
The same place may have very little rain during the dry season.
Some regions may experience floods while other regions face droughts.
This difference in water availability creates water shortages.
Seasonal rainfall means rainfall that changes during different seasons.
Annual rainfall means the total rainfall received in one year.
Water availability depends on both:
How much rain a place receives
When the rain falls
If rainfall is concentrated in only a few months, people must store water for the rest of the year.
As the population increases, the demand for water also increases.
More people need water for:
Drinking
Cooking
Cleaning
Toilets
Farming
Schools
Hospitals
Businesses
Industries
A growing population can put great pressure on rivers, lakes, and groundwater.
Agriculture uses a very large amount of water.
Farmers use irrigation when rainfall is not enough. Irrigation water may come from:
Canals
Wells
Tube wells
Rivers
Dams
Water scarcity becomes worse when farmers grow water-intensive crops in dry areas or use inefficient irrigation methods.
Flood irrigation, for example, may waste water because much of it evaporates or flows away. Drip irrigation and sprinkler irrigation use water more efficiently.
Industries need water for:
Washing raw materials
Cooling machines
Processing products
Generating power
Cleaning factories
Factories may also release chemical waste into rivers and groundwater. This can make water unsafe for people and animals.
Industrial growth therefore increases both water use and the risk of water pollution.
Urbanisation means the growth of towns and cities.
Cities require large amounts of water for:
Homes
Offices
Roads
Hospitals
Schools
Construction
Businesses
Concrete roads and buildings prevent rainwater from entering the ground. This reduces groundwater recharge and increases surface runoff.
Water pollution occurs when harmful substances enter water.
Sources of pollution include:
Sewage
Industrial waste
Fertilisers
Pesticides
Plastic
Oil
Domestic garbage
Polluted water may spread diseases, kill aquatic life, damage ecosystems, and become unsuitable for drinking or farming.
Pollution reduces the amount of freshwater that is safely available.
Water conservation means protecting water and using it carefully.
Ways to conserve water include:
Closing taps when water is not needed
Repairing leaking pipes
Using water-efficient appliances
Avoiding unnecessary wastage
Reusing water when possible
Using drip and sprinkler irrigation
Protecting ponds, lakes, and rivers
Planting trees
Preventing pollution
Rainwater harvesting means collecting and storing rainwater for later use.
Rainwater can be collected from:
Roofs
Courtyards
Roads
Open spaces
It can be stored in tanks or directed into the ground to recharge groundwater.
Rainwater harvesting is especially useful in areas where rainfall is seasonal or groundwater levels are falling.
Water management means planning how water will be collected, stored, used, shared, and protected.
Good water management includes:
Building reservoirs
Maintaining dams and canals
Recharging groundwater
Treating wastewater
Improving irrigation
Preventing pollution
Sharing water fairly
Protecting forests and wetlands
Water management must consider the needs of households, farmers, industries, animals, and future generations.
Dams are structures built across rivers to store and control water.
They can be used for:
Irrigation
Drinking water
Hydroelectricity
Flood control
Industrial water supply
Inland navigation
Fish production
Because they serve several purposes, they are called multipurpose projects.
However, dams can also cause problems. They may:
Displace local people
Submerge forests and villages
Damage ecosystems
Change the natural flow of rivers
Create conflicts between different users
Water is renewable because the hydrological cycle constantly recycles it.
However, usable freshwater is limited because:
Most water is salty
Freshwater is unevenly distributed
Groundwater may take a long time to recharge
Pollution makes water unusable
People are consuming water quickly
Therefore, water must be treated as a valuable resource.
Water conflicts happen when different groups or regions want to use the same water supply.
Conflicts may occur between:
States
Cities and villages
Farmers and industries
Upstream and downstream communities
People and large development projects
Fair sharing, proper planning, and cooperation are needed to solve water conflicts.
Earth has a huge amount of water, but only a small part is usable freshwater. The hydrological cycle renews water, yet water shortages still occur because of uneven rainfall, population growth, farming, industries, cities, pollution, and poor management.
The solution is to conserve water, prevent pollution, collect rainwater, recharge groundwater, use efficient irrigation, and manage water fairly. jess103.pdf
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