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Water
South Bank University Graphic
Water's chemical description is
H2O, that is one atom of oxygen bound to two atoms of hydrogen. The hydrogen
atoms are "attached" to one side of the oxygen atom, resulting in a
water molecule having a positive charge on the side where the hydrogen atoms
are and a negative charge on the other side, where the oxygen atom is.
Since opposite electrical charges
attract, water molecules tend to attract each other, making water kind of
"sticky." The side with the hydrogen atoms (positive charge) attracts
the oxygen side (negative charge) of a different water molecule.
- Water is unique in that it is
the only natural substance that is found in all three states -- liquid,
solid (ice), and gas (steam) -- at the temperatures normally found on Earth.
Earth's water is constantly interacting, changing, and in movement.
- Water freezes at 32o
Fahrenheit (F) and boils at 212o F (at sea level, but 186.4°
at 14,000 feet). In fact, water's freezing and boiling points are the
baseline with which temperature is measured: 0o on the Celsius
scale is water's freezing point, and 100o is water's boiling
point. Water is unusual in that the solid form, ice, is less dense than the
liquid form, which is why ice floats. Water contracts until it reaches 4 C
then it expands until it is solid. Solid water is less dense that liquid
water because of this.
- Water has a high specific heat
index. This means that water can absorb a lot of heat before it begins to
get hot. This is why water is valuable to industries and in your car's
radiator as a coolant. The high specific heat index of water also helps
regulate the rate at which air changes temperature, which is why the
temperature change between seasons is gradual rather than sudden, especially
near the oceans.
- Water has a very high surface
tension. In other words, water is sticky and elastic, and tends to clump
together in drops rather than spread out in a thin film. Surface tension is
responsible for capillary action, which allows water (and its dissolved
substances) to move through the roots of plants and through the tiny blood
vessels in our bodies.
- water's properties:
- Weight: 62.416 pounds per
cubic foot at 32°F
- Weight: 61.998 pounds per
cubic foot at 100°F
- Weight: 8.33
pounds/gallon, 0.036 pounds/cubic inch
- Density: 1 gram per cubic
centimeter (cc) at 39.2°F, 0.95865 gram per cc at 212°F
The
States of Water
Water
has three states. Below freezing water is a solid (ice or snowflakes), between
freezing and boiling water is a liquid, and above its boiling point water is a
gas.
Water
changing from solid to liquid is said to be melting. When it changes from liquid
to gas it is evaporating. Water changing from gas to liquid is called
condensation . Frost formation is when water changes from gas directly to solid
form. When water changes directly from solid to gas the process is called
sublimation.
Water
Measurements
1
gallon = 4 quarts = 8 pints = 128 ounces = 231 cubic inches
1 liter = 0.2642 gallons = 1.0568 quart = 61.02 cubic inches
1 million gallons = 3.069 acre-feet = 133,685.64 cubic feet
Source:
Three temperature scales
are in common use in science and industry.
Two of those scales are SI metric:
The degree Celsius (°C) scale was devised by
dividing the range of temperature between the freezing and boiling temperatures
of pure water at standard atmospheric conditions (sea level pressure) into 100
equal parts. Temperatures on this scale were at one time known as degrees
centigrade, however it is no longer correct to use that terminology. [In
1948 the official name was changed from "centigrade degree" to
"Celsius degree" by the 9th General Conference on Weights and Measures
(CGPM).]
The kelvin (K) temperature scale is an extension
of the degree Celsius scale down to absolute zero, a hypothetical
temperature characterized by a complete absence of heat energy. Temperatures on
this scale are called kelvins, NOT degrees kelvin, kelvin is not
capitalized, and the symbol (capital K) stands alone with no degree symbol. [In
1967 the new official name "kelvin" and symbol "K" were set
by the 13th General Conference on Weights and Measures (CGPM).]
The degree Fahrenheit (°F) non-metric
temperature scale was devised and evolved over time so that the freezing and
boiling temperatures of water are whole numbers, but not round numbers as
in the Celsius temperature scale.
Some baseline temperatures in the three temperature
scales:
| temperature
| kelvin
| degree Celsius
| degree Fahrenheit
|
| symbol
| K
| °C
| °F
|
| boiling point of water
| 373.15
| 100.
| 212. |
| melting point of ice
| 273.15
| 0.
| 32. |
| absolute zero
| 0.
| -273.15
| -459.67 |
|
Boiling
Points Of Water
|
| |
Altitude
(feet)
|
Boiling
Point |
|
Altitude (feet)
|
Boiling
Point |
| |
°F |
°C |
|
°F |
°C |
| |
-1000
|
213.8
|
101.0 |
|
5000
|
202.9
|
94.9 |
| |
-500
|
212.9
|
100.5 |
|
5500
|
201.9
|
94.4 |
| |
0
|
212.0
|
100.0 |
|
6000
|
201.0
|
93.9 |
| |
500
|
211.1
|
99.5 |
|
6500
|
200.1
|
93.4 |
| |
1000
|
210.2
|
99.0 |
|
7000
|
199.2
|
92.9 |
| |
1500
|
209.3
|
98.5 |
|
7500
|
198.3
|
92.4 |
| |
2000
|
208.4
|
98.0 |
|
8000
|
197.4
|
91.9 |
| |
2500
|
207.4
|
97.4 |
|
8500
|
196.5
|
91.4 |
| |
3000
|
206.5
|
96.9 |
|
9000
|
195.5
|
90.8 |
| |
3500
|
205.6
|
96.4 |
|
9500
|
194.6
|
90.3 |
| |
4000
|
204.7
|
95.9 |
|
10000
|
193.7
|
89.8 |
| |
4500
|
203.8
|
95.4 |
|
15000
|
184.0
|
84.4 |
Water
Distribution
One estimate of global
water distribution:
| Oceans,
Seas, & Bays |
1,338,000 |
96.5 |
- |
| Ice
caps, Glaciers, & Permanent Snow |
24,064 |
1.74 |
68.7 |
| Groundwater |
23,400 |
1.7 |
- |
| Fresh |
(10,530) |
(0.76) |
30.1 |
| Saline |
(12,870) |
(0.94) |
- |
| Soil
Moisture |
16.5 |
0.001 |
0.05 |
| Ground
Ice & Permafrost |
300 |
0.022 |
0.86 |
| Lakes |
176.4 |
0.013 |
- |
| Fresh |
(91.0) |
(0.007) |
.26 |
| Saline |
(85.4) |
(0.006) |
- |
Atmosphere
|
12.9 |
0.001 |
0.04 |
| Swamp
Water |
11.47 |
0.0008 |
0.03 |
| Rivers |
2.12 |
0.0002 |
0.006 |
| Biological
Water |
1.12 |
0.0001 |
0.003 |
| Total |
1,385,984 |
100.0 |
100.0 |
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About
3,100 cubic miles of water, mostly in the form of water vapor, is in
the atmosphere at any one time. If it all fell as precipitation at
once, the Earth would be covered with only about 1 inch of
water.
-
The
48 contiguous United States receives a total volume of about 4 cubic
miles of precipitation each day.
-
Each
day, 280 cubic miles of water evaporate or transpire into the
atmosphere.
-
Of
the freshwater on Earth, much more is stored in the ground than is
available in lakes and rivers. More than 2,000,000 cubic miles of
fresh water is stored in the Earth, most within one-half mile of the
surface. Contrast that with the 60,000 cubic miles of water stored
as fresh water in lakes, inland seas, and rivers. The most is stored
in the 7,000,000 cubic miles of water found in glaciers and icecaps,
mainly in the polar regions and in Greenland.
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Glaciers and icecaps
cover about 10% of the world's landmass. These are concentrated in
Greenland and Antarctica and contain ~70% of the world's freshwater.
Unfortunately, most of these resources are located far from human
habitation and are not readily accessible for human use.
According to the United
States Geological Survey (USGS), 96% of the world's frozen freshwater is
at the South and North poles, with the remaining 4% spread over 550 000
km2 of glaciers and mountainous icecaps measuring about 180 000
km3 (UNEP, 1992; Untersteiner, 1975; WGMS, 1998, 2002).
Groundwater is by
far the most abundant and readily available source of freshwater, followed
by lakes, reservoirs, rivers and wetlands:
- Groundwater represents
over 90% of the world's readily available freshwater resource (Boswinkel,
2000). About 1.5 billion people depend upon groundwater for their
drinking water supply (WRI, UNEP, UNDP, World Bank, 1998).
- The amount of
groundwater withdrawn annually is roughly estimated at ~600-700 km3,
representing about 20% of global water withdrawals (WMO, 1997).
- A comprehensive picture
of the quantity of groundwater withdrawn and consumed annually around
the world does not exist.
Reservoirs are
artificial lakes, produced by constructing physical barriers across
flowing rivers, which allow the water to pool and be used for various
purposes. The volume of water stored in reservoirs worldwide is estimated
at 4 286 km3 (Groombridge and Jenkins, 1998)
Wetlands include
swamps, bogs, marshes, mires, lagoons and floodplains. The 10 largest
wetlands in the world by area are:
- West Siberian
Lowlands (780 000-1 000 000 km2)
- Amazon River (800 000
km2)
- Hudson Bay Lowlands (200 000-320 000
km2)
- Pantanal (140 000-200 000
km2)
- Upper Nile River (50 000-90 000
km2)
- Chari-Logone River (90 000
km2)
- Hudson Bay Lowlands in
the South Pacific (69 000 km2)
- Congo River (40 000-80 000
km2)
- Upper Mackenzie River
(60 000 km2)
- North America prairie
potholes (40 000 km2)
The total global area of
wetlands is estimated at ~2 900 000 km2 (Groombridge and
Jenkins, 1998). Most wetlands range in depth from 0-2 metres. Estimating
the average depth of permanent wetlands at about one metre, the global
volume of wetlands could range between 2
Most freshwater lakes
are located at high altitudes, with nearly 50% of the world's lakes in
Canada alone. Many lakes, especially those in arid regions, become salty
through evaporation, which concentrates the inflowing salts. The Caspian
Sea, the Dead Sea, and the Great Salt Lake are among the world's major
salt lakes. |
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Credit:
EPA, UNEP, USGS, NASA
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