Experiment I – Water Purification Through Water Cycle
Exploration 1: Purifying Water through the Hydrological Cycle
You might be familiar with the hydrological cycle, technically known as the water cycle. Have you ever contemplated the advantages it brings through the continuous movement of water across, above, and beneath the Earth’s surface? Within the hydrosphere, water changes between liquid, vapor, and ice states. The shift from liquid to vapor is called evaporation. When the air cools, this vapor condenses in clouds and then falls to the earth, where it is absorbed in various ways. It can be taken up by plants, held in surface water bodies such as lakes, rivers, and seas, or evaporated by sunlight. Alternatively, it may seep into the soil or flow through it as groundwater over time. The water that plants use can return to the earth through transpiration, a process where moisture is transported from the roots to the tiny pores on the underside of leaves, turning into vapor and released into the atmosphere. You may question this process since you don’t see plants sweating. The lack of visible water doesn’t mean it isn’t being released into the air. During the growing season, a single leaf can transpire an amount of water much greater than its own weight. For example, a mature oak tree can transpire up to 40,000 gallons each year! Substances like salt, dissolved in the water, are left behind when the vapor condenses back into liquid, yielding relatively pure water. Evaporation and condensation are key in water purification. These natural processes not only happen in the water cycle but can also be utilized to purify water for drinking or industrial use. Water is continually in motion, driven by solar energy and gravity. Try this simple experiment at home to understand how the water cycle aids in water purification.
NECESSARY MATERIALS:
- 4 cups of soil or sand
- 12 stones
- 2 quarts of water
- A large glass bowl with high sides (like a mixing bowl)
- A short glass
- Clear plastic wrap
- A sunny day
RELATED LINKS:
EXPERIMENT II – Non-Point Source Pollution
EXPERIMENT III – The Role of Plants in Water Filtration
METHOD:
Mix the soil (or sand) with water in the large bowl. Place an empty, clean short glass in the center of the bowl. Set the bowl outside in the sunlight. Cover it with plastic wrap, anchoring the edges with the stones, and place one stone directly over the glass. Allow the bowl to sit in the sun for several hours. Notice the water collected in the glass (it should be mostly free of sediment) and the dried soil in the bowl.
FOLLOW-UP QUESTIONS:
- What are the two essential processes in water purification? (Evaporation and Condensation)
- Where else can condensation be observed? (On a cold drink container outside on a warm day)
- How does this process work on Earth?
- What does the plastic wrap represent? (Our atmosphere)
- What is condensation? (Clouds and rainfall)
- What would happen if the plastic wrap were dirty? (It would imitate air pollution)
VARIATIONS:
Add food coloring to the water to demonstrate that this process does not remove all impurities. This can be done alongside the experiment described above.
Source: Environmental Protection Agency
RELATED LINKS:
EXPERIMENT II – Non-Point Source Pollution
EXPERIMENT III – The Role of Plants in Water Filtration