HOW MUCH WATER IS THERE?
Board of Water and Soil Resources
394 South Lake Avenue Room 403
Duluth, MN 55802
Level: Grades 4-7
Estimated time required: Preparation
Activity time 5 minutes
Anticipated learning outcomes
- To demonstrate how little freshwater is available for
- To introduce the concept of a limited water supply and
the need to protect water resources.
This works well in an informal outdoor setting or in a classroom. It is
a brief demonstration that can serve as an introduction to other environmental
activities related to water resources.
- Container with one gallon of water (an ice cream pail
- Clear, one-cup measure or a beaker marked with 1/2 cup
- Explain that the gallon of water represents all the water
on the earth. Ask students how much of the earth is covered by water (most
older students will know 70-75%). Remind them that the majority of water
is salt water found in the oceans. Ask them to estimate how much of the
gallon would represent all the freshwater on earth.
- Pour out 1/2 cup of water. This represents all the fresh
water on earth; all the rest is salt water. Less than 3% of all the water
on earth is freshwater. Explain that this 1/2 cup represents all the water
found in lakes, rivers, underground, frozen in ice, as well as all the
water found in living things (plants and animals - including the students
themselves!). Ask students to estimate how much of that 1/2 cup of water
is available for us to use.
- Use the eyedropper to drip one drop of water out of the
1/2 cup measure. This is all the freshwater available for our use. Two
thirds of the water in the cup represents water frozen as ice, much of
the rest is unreachable as deep groundwater, or is bound up as soil moisture,
biomass, or in the atmosphere.
Results and Discussion
- Explain that all the water on earth now is the same water
that has been here since the dinosaurs lived and that it's all the water
we'll have in the future, too. No "new" water is being made.
If we don't take care to protect Earth's limited water resources, we'll
have to live with polluted water or pay to clean it up.
- All water is part of the hydrologic cycle, a repeating
pattern of evaporation, transport, and precipitation, punctuated with storage
periods when the water remains in oceans, lakes, groundwater, atmosphere,
or trapped in polar ice caps. These periods may range from a few days in
the atmosphere to thousands of years in the ocean. Those numbers are average
residence times for individual water molecules - not every drop of water
will stay that long and some will be "out of circulation" much
longer. Molecules may remain in polar ice for tens of thousands of years.
The table below lists commonly accepted percentages for
where water is found on Earth. These numbers may vary from other sources
you see. The difference occurs because some sources include the water that
is part of the chemical compositions of rocks and minerals.
|EARTH'S WATER SUPPLY|