The concepts developed in this standard include
Water's Unique Properties
- Water is the
only compound that commonly exists in all three states (solid, liquid, gas) on Earth.
The unique properties of water are a major factor in the ability of our planet to
- Among water’s unique properties is that one side of each water molecule is
negative and the other is slightly positive.
- Individual water molecules, therefore, attract other water molecules like little magnets as the slightly positive portion of a water molecule
is attracted to the slightly negative portion of an adjacent water molecule. In this way water
molecules “stick” together. (The shape of water molecules
give it adhesive and cohesive properties.)
- A large number of substances will “dissolve” in water. For this reason, water is often called the
- Water is able to absorb heat energy without showing relatively large changes
in temperature. Large bodies of water act to moderate the climate of surrounding
areas by absorbing heat in summer and slowly releasing that heat in the winter.
For this reason, the climate near large bodies of water is slightly
areas without large bodies of water. (This explains why cities and
counties along the Chesapeake Bay and Atlantic coast have average winter temperatures
that are milder than areas in central and
- Additional properties of water are its high surface tension and the
large range of temperature (0 – 100 degrees Celsius) in which it can be
found in the liquid state, as well as the fact that, unlike other substances,
it expands when it freezes. Ice is less dense than liquid water. (Ice
Water's Role in Physical and Chemical Weathering
- Water (rain, ice, snow) has shaped our environment by physically and
chemically weathering rock and soil
and transporting sediments.
- Freezing water can break rock without any change in the minerals that form
the rock (physical weathering).
This usually produces small particles and sand.
- Water with dissolved
gases and other chemicals causes the minerals in rocks to be changed, leading to the deterioration
of the rock (chemical weathering).
- Examples of chemical weathering:: acidified water on building material such as concrete, limestone, or marble causes chemical
Water's Important Historical Role
- Scientific evidence indicates that the Earth formed about
four-and-a-half billion years ago from the dust and debris orbiting the sun.
- Due to gravity, this debris became compacted and grew quite hot, creating hot
gases including water vapor and carbon dioxide. Over millions of years,
the Earth and its gases cooled and seas are believed to have formed when the Earth cooled enough for water vapor in the atmosphere to condense.
- Most of Earth's water is salt water in the oceans (97%).
Available non-frozen, fresh water makes up less than
- Water occurs on our Earth in oceans, lakes, rivers, streams,
and in rock layers underground called aquifers.
A large amount of water is also found in the bodies of living things.
- The first human settlements were established by springs, rivers, and lakes.
Reliable fresh water sources and irrigation
systems, allowed civilizations to grow and flourish.
As cities grew, different strategies were employed to collect water
(tunnels, aqueducts, wells, cisterns, pumps, reservoirs).
Water for Irrigation, Power Generation
- Water is essential for agriculture. Crops watered by reliable
irrigation systems are more productive, and harvests more dependable.
- Water is an important resource used in power generation. Hydroelectric
power plants make use of the kinetic energy of water as it flows through turbines.
Water is also used in power plants as the water is heated and turned to steam.
The steam is used to turn turbines
that generate electricity.
Clean Water and Health
- In the past, streams and rivers were often used to dispose of human
waste, and open sewers were
common. During the mid-1800s public health officials recognized the connection between
disease outbreaks and contamination of public wells and drinking water. Advances in
water treatment and sanitary sewers have helped
eliminate diseases associated with human waste.