WATER
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Water Water Everywhere But Nary a
Drop to Drink (Coleridge.Rime of the
Ancient Mariner)
Earth’s surface – 70% water
97% of water in oceans: salt water
3% is fresh water
25% of fresh water is groundwater
75% of fresh water is in ice and glaciers
Only .03% of water is available to us: in
atmosphere, streams, rivers, wetlands, lakes
• (Some is lost to pollution)
DESALINATION
• DISTILLATION
– Water boiled, steam is condensed, salt left behind, (brine liquid).
– Requires much energy
REVERSE OSMOSIS
- Water forced through impermeable membrane
- Salt left behind (brine liquid)
CONSEQUENCES
- Salt deposits on land harm plants and animals
- Dumped in bay or coastal areas harms fish and aquatic life
WATER USAGE
• How do we consume water?
– Agriculture 70%, Industry 20%, households 10%
• Why do we put drinking water in our toilets?
• What is grey water and contaminated water?
– Gray water: showers, washing machines, bathroom
sinks – can be used for watering plants, washing cars,
flushing toilets
– Contaminated water – from toilet, kitchen sinks,
dishwashers
VIRTUAL WATER
PROPERTIES OF WATER
• Liquid, solid, and gas—at the temperatures found
on Earth.
• Universal Solvent – dissolves more substances
than other liquid: carries valuable chemicals,
minerals and nutrients through ground and our
bodies.
• pH is neutral 7 (neither acidic or alkaline)
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Water Density
• When cooled from room temperature, liquid water becomes
increasingly dense (as with other substances.)
• However, at 4C or 39F pure water reaches its maximum
density and then starts to expand and becomes less dense
• This is why ice floats. If not the bottom of our lakes would
freeze.
• High water density allows sound to move through it over long
distances (important for whales).
PROPERTIES OF WATER
• HIGH SPECIFIC HEAT INDEX
• – absorbs a lot of heat before it gets hot.
– Makes a good coolant in car radiators and for industry
– Regulates rate at which air changes temperature so temperature
change between seasons is gradual.
AIR PRESSURE AFFECTS
Boiling point at sea level is 212 F; at 5000 ft. 202.9 F (With less
atmospheric pressure it takes longer to boil an egg)
CONDUCTIVITY
Pure water does not conduct electricity until it has dissolved the
inorganic substances around it. (positively or negatively charged ions)
A failing sewage system would raise the conductivity because of the
presence of chloride, phosphate, and nitrate; an oil spill would lower
Conductivity of Water
Pure water does not conduct electricity until it has dissolved
the inorganic substances around it.
E.g. chloride, nitrate, sulfate, and phosphate anions (ions that
carry a negative charge) or sodium, magnesium, calcium,
iron, and aluminum cations (ions that carry a positive
charge).
Organic compounds like oil, phenol, alcohol, and sugar do not
conduct electrical current very well and therefore have a low
conductivity when in water.
A failing sewage system would raise the conductivity because
of the presence of chloride, phosphate, and nitrate; an oil
spill would lower the conductivity.
SURFACE TENSION
• Water has a very high surface tension, a property of the
surface of a liquid that allows it to resist an external force.
• COHESION: water molecules attracted to other water
molecules creates the thin “skin” along the surface of water
Surface tension:
– Allows water striders to “walk on water”
ADHESION: water molecules attracted to other materials.
- Allows the capillary action that carries water and its dissolved
substances to move through the roots of plants and through the
tiny blood vessels in our bodies.
FOAM IN LAKES AND STREAMS
• Foam accumulates against logs, banks of streams, lake
shores. Starts out white, turns brown
• Surfactants (either anthropogenic: e.g.detergents,
shampoos, or naturally produced from algae and
plants) are molecules that are called surface active
agents that interact with water reducing the surface
tension
• Foam is produced as air, introduced in the turbulence
of stream riffles .... bubbles to the water surface where
surface tension has been reduced.
• Foam is not always a sign of pollution