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E. T. A LOCAL WAY OF LEARNING


Title: WATER DESALINATION

Author: Jane Ducey
Eulalie R. Rivera Elementary School

Grade Level: 4-6

Concepts: Disciplines:
1. The Sun 1. Social Studies
4. Clean Water 2. Science
6. Natural Resource
9. Man Changes World

Objective:
Student shall, through sense of taste, demonstrate that the sun's
energy changes only the water molecules into vapor and leaves the salt
behind. There is not enough heat to effect the change of phase of the
salt molecules.

Rationale:
Like the Ancient Mariner of Colridge, we live surrounded by water but
are frequently in dire need of fresh water. Small islands lacking
sufficient ground water for wells are dependent upon the rain catchment
method, barging of fresh water from another place or desalination of
sea water for their supply of fresh water. The desalination of salt
water can be achieved at the elementary level without the side-arm
flask and condensation tube of a conventional distillation set-up.

Materials Needed:
A set of glass or plastic bowls: one large pie-plate shape, one small
and one dome shaped but with a smaller diameter than the pie plate. See
diagram below.

Directions/Activity:
Out-of-doors on a sunny day set up the still, after all students are
assured that the small bowl contains sea water. The bowls must be in
direct sunlight or under the desk lamp of sufficient heat indoors. In a
short time the domed bowl will show the mist of condensation followed
by the evidence of water trickles running down the inside of the dome
into the catchment vessel. A breeze blowing on the dome serves to cool
it.




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E.T.


WATER DESALINATION

While the processes of evaporation and condensation are taking place in
the bowls, teach or review the water cycle, stressing the fact that
only the pure water will be vaporized by the sun's heat. Late in the
day enough water will have accumulated in the bottom dish to sample for
freshness by tasting it.

Discussion and Suggested Projects:
How does your demonstration unit compare with a commercial desalination
plant?

Do research in the library.
You might visit a large water desalinator and have a plant employee
explain the procedure for providing fresh water to your town.

Discuss the feasibility and problems of laying a pipe line from Puerto
Rico to St. Thomas to bring in fresh water instead of the barge which
now brings it on an emergency basis.

Invite a person from Public Works to give you more information about
the water catchments built on the mountainsides. What are the problems
and limitations of these long-standing facilities?