OBJECTIVES:

·         Analyzing why water cycle is a natural filtration system.
 ·         Experimenting with filtration.


VOCABULARY:       

·         solvent
 ·         condensation
·         evaporation
 ·         filtration
 ·         precipitation
 ·         water cycle

MATERIALS:
·         Giving Water a Second Chance by J. R.Blueford
·         Funnels
·         Beakers
 ·         Erlenmeyer flask
·         Sand (coarse and fine)
·         Dirt from garden
·         cottonballs


BACKGROUND:

Water is our most common natural resource.  It is essential to the biology and chemistry of all living things, it plays a major role in shaping the earth and is an active agent in many physical reactions. It is important to most life to keep it clean.

There is plenty of water on Earth, but 97% of this water is saline (contains dissolved salts).  Only 3% is fresh and about two thirds of that amount is locked up in polar ice caps and glaciers; about one third can be found as ground water, lakes, and in the atmosphere.

Water exists in three states of matter:  solid (ice), liquid (water), and gas (vapor) at normal conditions.  Water is a colorless, odorless, tasteless liquid with a melting point of 0° centigrade and a boiling point of 100° centigrade.  

Water can be easily cleaned through the water cycle.  When water evaporates in the gaseous phase, it leaves all the impurities behind.  Water can also be cleaned through other natural ways.  Humans have created ways in which they can also clean water without going through a natural water cycle.

PROCEDURE:  

1.      Discuss with students the following major points about water or the hydrologic cycle.  Draw the diagram of the water cycle.

Goal of this section is for students to see a variety of ways that the water cycle naturally purifies water through evaporation, transpiration and infiltration. 

  • A. Water precipitates from clouds as rain, snow, sleet, or hail to the Earth’s surface.
  • B. Depending on a number of factors such as soil type, slope, moisture conditions, and intensity of precipitation will either infiltrate into the ground or runoff into rivers and streams. Infiltrate means the water sinks into the ground.
  • C. Virtually no water infiltrates through paved roads and parking lots, so almost all of it becomes urban runoff. Runoff from rivers, and streams is stored in large bodies of water such as lakes, estuaries, and oceans.
  • D. Water is returned to the atmosphere evaporation from the surface of land or water bodies, or through plants by a process called transpiration.
  • E. Clouds are formed by condensation of water vapor that evaporated from the land or oceans.

2.      Hopefully this diagram should be familiar to students and they should be able to tell you about each of the components.  Ask them which are human-made portions of the water cycle? (Reservoir, dams and canals.)  Where does a spring get its water supply?  (Usually from the ground water percolating up.)  Where does water from the mountains wind up?  (The oceans.)  Which is the newest water? (Rain) Oldest? (Oceans.) 

3. Read “Give Water a Second Chance”  so students can see how the water cycle has been cleaning water for eons of time, but now people can clean it also with different methods. Do experiments with filtering dirty water using a cotton ball, cotton ball with course sand and a cotton ball with fine sand.  (for cleanup, at end of lesson be sure to dump dirty sandy water in the garden, not down the sink).

  • A. Give students a beak with about 150 ml of water, mix in about 5 ml of “dirt” from the school ground and stir to make dirty water.
  • B. Use funnels and put a cotton ball in the base of the funnel so it sticks part way into the funnel part.
  • C. First have the student just pour dirty water into the funnel with the cotton ball and see how much is “cleaned”
  • D. Make another dirty mixture and repeat the experiment but use 75 ml of the course sand on top of the cotton ball.
  • E. Make more dirty water and this time use a cotton ball in the filter and add 75 ml of fine sand. Did one work better than another?
  • F. Then have them re-pour the water from the last filtration over the fine sand again to see if they can filter it even more. (does the water get even clearer?)
  • G. Set out coarse sand, fine sand and more cotton and some powdered clay. Set the students free to experiment to try to figure out how to get the cleanest most filtered water. For example, they can try layering the sands and clay, or pour dirty water through multiple times.
  • H. Discuss results with students. How did they get the cleanest water?

Go back to the diagram of the water cycle and have them note infiltration has water going through deep dirt and rock deposits.  Filtration produces very clean water but it takes a long time.  Sometimes 100s of years! 

We should never waste water!

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