Childrens Illustrated Encyclopedia

557

Water

Water falls as rain and

is collected in lakes

and reservoirs.

Water is cleaned in

a treatment plant.

Once the water is

treated, it is pumped

up into a high tank,

ready to be used.

Water treatment

Water in a reservoir is usually not fit to

drink. It must pass through a treatment

center, which removes germs and other

harmful substances. Chlorine gas is

often dissolved into the water to kill

bacteria and viruses. In addition, the

water is stored in huge basins so that

pieces of dirt sink to the bottom; filters

made of stones and sand remove any

remaining particles.

SolutionS

Pure water is rarely

found in nature

because water dissolves

other substances to

form mixtures called

solutions. For example,

seawater is salty because

there are many

minerals dissolved in it.

Water solutions are

vital to life; blood

plasma, for instance,

is a water solution.

The sugar

disappears

when it is

completely

dissolved.

Sugar

dissolves

in water,

making

a sweet-

tasting sugar

solution.

Water Pressure

Water rushes out of a faucet because

it is under pressure; that is, it is

pushed from behind. Pressure is

produced by pumps that force water

along using pistons or blades like

those on a ship’s propeller. Water

pressure is also created by the sheer

weight of water above. the deeper

the water, the greater the pressure. If

you dive into a pool, you can

feel the water pressure

pushing on your

eardrums.

Fire fighters

connect their hoses

to fire engines,

which contain

powerful pumps.

The pumps

increase the

pressure so

that the water

can reach

flames high up

in buildings.

HydroeleCtrIC PoWer

People have used water as a source of power for more than 2,000

years. today, water is used to produce electricity in hydroelectric

(water-driven) power stations. Hydroelectric power stations are

often built inside dams. Water from a huge lake behind the dam

flows down pipes. the moving water spins turbines, which drive

generators and produce electricity. Hydroelectric power produces

electricity without causing pollution or using scarce resources.

With the water high above the

ground, the faucet can be turned

on so the water runs out.

Water tank

stores clean

water.

Underground water supplies

exist below the surface of

Earth. After a drought,

these supplies dry

out; it may take

years for them

to be refilled.

PollutIon and drougHt

In many places, such as east africa, there

is insufficient rain and constant drought.

Plants cannot grow, and people and

animals must fight a constant battle

for survival. Fresh, clean water can

also be difficult to obtain even

in places with lots of rain. this

is because waste from cities

and factories pollutes

the water, making it

unsafe to drink.

If three identical holes are

drilled in the side of a water-

filled container, water spurts out

much farther from the

lowest hole because

of the weight of the

water above.

Find out more

electricity

Heat

lakes

oceans and seas

rain and snow

rivers

Water can provide an unlimited supply

of power, unlike underground

resources such as

coal and gas.

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