Chapter 20 Water

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22 Φεβ 2014 (πριν από 3 χρόνια και 3 μήνες)

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Chapter 20

Water

1

Section 20.1


Uses for Water


Water should be used wisely!


Droughts, natural disasters, floods and low precipitation can
leave entire communities without fresh water.


Unpotable

= water that is
unsafe

to drink.



Residential use


Average person in U.S. uses about
300 L

of water
daily
.



2

Estimated U. S. Household Water Use

Activity

Daily Consumption

Brushing Teeth

19
-
39 L (faucets running)

Shaving

39
-
58 L (faucets running)

Washing

hands and face

4
-
8 L (faucets running)

Showering

75
-
80 (faucets running)

Bathing in tub

96
-
116 L (full tub)

Machine dishwashing

56
-
60 L (full

cycle
)

Dishwashing by hand

75
-
80 L (faucets running)

Clothes washing

140
-
170L (full

cycle
)

Toilet flushing

16
-
21 L (per flush)

3

Industrial Use


About
44 %

of all
freshwater

is used by
industry
.


Used to transport goods, dispose of wastes, power source,
manufacturing products and as a coolant.


Agricultural Use


Almost
half

of all freshwater in the U.S. is used by
agriculture
.


More than
200 billion L
each day is used for the irrigation
of farmland.


Irrigation



the process of bringing water to an area for use
in growing crops.
Wastes

a lot of water.



Section 20.1


Uses for Water

4

Effects of water use on ecosystems


Mono Lake
in CA


A saltwater lake fed by streams that carry melt
-
water from
surrounding mountains.


In 1940, Los Angeles began diverting the melt
-
water that fed
Mono Lake to other areas.


The
water level

is now
dropping

and the
salt concentration
is
increasing

to where it may be unable to support the organisms
living in the water.




Section 20.1


Uses for Water

5

Water uses in the U. S.

47%

Agriculture
Industrial
Residential
44%

9%

6

Surface Water


Water
above

the
ground

in streams, lakes and ponds.


Runoff



the water resulting from rainfall, melting glaciers
and snow and ice.


The water that
does not seep
into the ground.


It
flows down
a slope over land.



Section 20.2


Water Resources

7

Aquifers


The water that does not flow as runoff seeps down through
the spaces between soil particles.


Water that fills the spaces between soil particles is called
soil water
.


The water continues to seep further in the ground
becoming
groundwater
.


Section 20.2


Water Resources

8


Ground water now saturates the layer of bedrock also
known as the
water table
.


Beneath the water table is the
zone of saturation
, also
known as an
aquifer
.


Aquifer

is a layer or porous rock that contains water.


9

Section 20.2


Water Resources

Water Resource Problems


Overdraft



when a body water is drained faster than it is
filled.


Can lead to saltwater
intrusion



Can lead to
subsidence

(sinking land).


The
rising

of the
water table
level becoming closer to the surface.


Aquifer depletion
is occurring in very arid regions because it takes a really
long time
to recharge the water (get it back).

10

Section 20.2


Water Resources


Water is treated in order to remove any
impurities
.


Safety checks monitor the
quality

of water.


Tap water is not considered safe in much of South America,
Mexico, China and parts of Africa.



11

Section 20.3


Water Treatment


Some nations seek
alternative

sources of fresh water.


They may look to seas, salt lakes, or oceans for water.


Desalination



the process by which
salts

are removed
from water.


Can be used for drinking, cooking and irrigation.


12

Section 20.3


Water Treatment


3 most common methods of
desalination
:


1.
Distillation



salt water is
heated

to boiling, water is

evaporated, but the salt remains. Water
vapor

is

cooled and the fresh
liquid

water is collected.


2.
Reverse Osmosis


salt water is forced through a

strainer

that
traps

the salt and lets the fresh water

pass. The pores are large enough for water to pass but

too small for salt.

13

Section 20.3


Water Treatment


3.
Freezing



salt water is frozen. As it freezes, it

separates
, forming ice and a brine slush. The ice can

be
melted

to obtain fresh water.


Water
Purification



removes harmful
chemicals

and
microorganisms

that make the water
unpotable
.


-

It involves:



Sedimentation



Filtration



Aeration



Sterilization


14

Section 20.3


Water Treatment


Sedimentation and Filtration


Screens

are used to trap and remove
debris

that floats or is
suspended in water.


Enters a
settling tank
, where it is allowed to stand undisturbed.


As the water stands, particles suspended in the water settle to the
bottom as
sediment
.


Coagulants


chemicals

added to the water to aid in the settling
process.


Causes fine particles to
clump together
.


Water is drained from the settling tank and is then passed through
filters
.


15

Section 20.3


Water Treatment


Aeration and Sterilization


Used to treat water for
taste
,
odor
, and
bacteria
.


Aeration



the exposure of water to
air
.


Bacteria

is added to break down organic matter still present.


Oxygen

is added to the water to help purify it.


Sterilization



used to
kill

the
bacteria

that was previously
added.


Use extreme
heat and/or chemicals
.


Chlorine

and ozone most commonly used.


Fluoride

is added to help prevent tooth decay.


16

Section 20.3


Water Treatment


17