Page 158 - Volt Elevate The World Around Us Book 4

Oceans and seas are very large water bodies.

They contain salty water. A sea is smaller
than an ocean. There are many seas on the
earth.

ocean

It is not safe to drink water directly from natural sources for many reasons.
y Rainwater cannot be consumed as it has many dissolved gases, dust particles and
germs in it.

y Water bodies like lakes, rivers and ponds get polluted due to human activities like
garbage disposal, washing and bathing. Factories also release toxic wastes into them.
All this makes water in these water bodies unfit for drinking.

y Rivers that flow down mountains carry mud and other waste materials along with
them. Hence, we cannot drink water directly from them.

y Seawater is not fit for drinking because it is salty.

Dams, Reservoirs and Canals

Dams are walls built across rivers to block or control the flow of water. From dams, water
is collected in artificial lakes called reservoirs. It is released when the level of water in

the river decreases. It is also used for various other things like generating electricity.
Canals are dug as channels to send water from rivers or reservoirs to agricultural areas
for irrigation.

The Water Cycle – Evaporation and Condensation

Let’s understand the process of evaporation and condensation.

Evaporation

On a rainy day, a few hours after the rain stops

and the sun comes out, the puddles of water
disappear. This happens due to the heat of

the sun. On heating, water changes into water
vapour and moves up. This is called evaporation.

drying of clothes in the sun

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