WATER

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WATER
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Just some facts

• 70 of the Earth is covered in water
• Oceans hold 97 of the Earths water
• Freshwater only constitutes 3
• Of that freshwater most is trapped in glaciers
  and ice caps
• The rest is found in groundwater, lakes, soil
  moisture, atmospheric moisture, rivers and
  streams.

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WATERS IMPORTANCE, AVAILABILITY, AND RENEWAL

• Water keeps us alive, moderates climate, sculpts
  the land, removes and dilutes wastes and
  pollutants, and moves continually through the
  hydrologic cycle.
• Only about 0.02 of the earths water supply is
  available to us as liquid freshwater.

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WATERS IMPORTANCE, AVAILABILITY, AND RENEWAL

• Comparison of population sizes and shares of the
  worlds freshwater among the continents.

Figure 14-2
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Populations and water supply

• Human settlements are determined by the
  availability of freshwater.
• high precipitation and small populations equals
  highest per capita (Iceland, Norway)
• Lowest per capita Low precipitation and highest
  populations (Egypt, Israel)
• In the US freshwater 500,000 gallons per person
  per year.

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WATERS IMPORTANCE, AVAILABILITY, AND RENEWAL

• Some precipitation infiltrates the ground and is
  stored in soil and rock (groundwater).
• Water that does not sink into the ground or
  evaporate into the air runs off (surface runoff)
  into bodies of water.
• The land from which the surface water drains into
  a body of water is called its watershed or
  drainage basin.

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WATERS IMPORTANCE, AVAILABILITY, AND RENEWAL

• We currently use more than half of the worlds
  reliable runoff of surface water and could be
  using 70-90 by 2025.
• About 70 of the water we withdraw from rivers,
  lakes, and aquifers is not returned to these
  sources.
• Irrigation is the biggest user of water (70),
  followed by industries (20) and cities and
  residences (10).

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Salinity

• The saltiness.

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Importance

• Leonardo da Vinci said that Water is the driver
  of nature. Without water, the other nutrient
  cycles would not exist in their present forms,
  and current forms of life on earth could not
  exist.

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Water
H
H
O
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Water

• A water molecule (H2O), is made up of three atoms
  --- one oxygen and two hydrogen.

O
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Water

• About 60-90 percent of an organism is water

Water is called the universal solvent
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Water Properties

• Polarity

• Cohesion

• Surface Tension

• Adhesion

• High Specific Heat

• High Vaporization

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Water is Polar

• In each water molecule, the oxygen atom attracts
  more than its "fair share" of electrons
• The oxygen end acts negative
• The hydrogen end acts positive
• Causes the water to be POLAR
• However, Water is neutral (equal number of e- and
  p) --- Zero Net Charge

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Hydrogen Bonds Exist Between Water Molecules

• One hydrogen bond is weak , but many hydrogen
  bonds are strong

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Cohesion

• Attraction between particles of the same
  substance (water is attracted to itself)
• Results in Surface tension
• Produces a surface film on water that allows
  insects to walk on the surface of water

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Cohesion
Helps insects walk across water
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Adhesion

• Attraction between two different substances.
• Water will make hydrogen bonds with other
  surfaces such as glass, soil, plant tissues, and
  cotton.
• Capillary action-water molecules will tow each
  other along when in a thin glass tube.
• Example transpiration process which plants and
  trees remove water from the soil, and paper
  towels soak up water.

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Adhesion Causes Capillary Action
Which gives water the ability to climb
structures
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Adhesion Also Causes Water to
Attach to a silken spider web
Form spheres hold onto plant leaves
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High Specific Heat

• Amount of heat needed to raise or lower 1g of a
  substance 1 C.
• Water resists temperature change, both for
  heating and cooling.
• Water can absorb or release large amounts of heat
  energy with little change in actual temperature.

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High Heat of Vaporization

• Water's heat of vaporization is 540 cal/g.
• In order for water to evaporate, each gram must
  GAIN 540 calories (temperature doesnt change ---
  100oC).
• As water evaporates, it removes a lot of heat
  with it (cooling effect).

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Hydrologic Cycle
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