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Water from Thin Air: Experimenting with Dew Traps

Difficulty
Time Required Long (2-4 weeks)
Prerequisites None
Material Availability Readily available
Cost Low ($20 - $50)
Safety Minor injury is possible. Use caution when digging holes with the shovel. Don't drink any of the water that you collect in the dew traps.

Abstract

Most of us live in areas where sources of water exist nearby as oceans, rivers, lakes, ponds, streams, reservoirs, wells, or even underground streams. But in some places, like the desert, water is hard to find and a precious resource. In this environmental engineering science project, you will investigate one way that people living in arid regions can collect water inexpensively: dew traps.

Objective

To build two dew traps of different diameters and determine how the amount of water collected depends on the surface area of the trap.

Credits

Michelle Maranowski, PhD, Science Buddies

Cite This Page

MLA Style

Science Buddies Staff. "Water from Thin Air: Experimenting with Dew Traps" Science Buddies. Science Buddies, 16 Feb. 2013. Web. 27 Nov. 2014 <http://www.sciencebuddies.org/science-fair-projects/project_ideas/EnvEng_p034.shtml>

APA Style

Science Buddies Staff. (2013, February 16). Water from Thin Air: Experimenting with Dew Traps. Retrieved November 27, 2014 from http://www.sciencebuddies.org/science-fair-projects/project_ideas/EnvEng_p034.shtml

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Last edit date: 2013-02-16

Introduction

Deserts are defined as landscapes that receive on average less than 10 inches (about 250 millimeters) of precipitation (either rain or snow) per year. For people who live in the desert or in semi-arid regions, which receive between 10 inches and 20 inches of precipitation on average per year, finding water can mean the difference between life and death. You may not see water in the form of a lake or stream in a desert, but that doesn't mean that water isn't present in the environment. Water vapor in the air, also known as humidity, comes from water evaporating (changing from liquid to gas) from oceans, lakes, and other bodies of water, and water vapor excreted by the leaves of plants through a process called transpiration. Water also exists in the form of dew, small droplets of water that form on surfaces during the night. As the nighttime air cools to a point where it can't hold any more water vapor, the vapor condenses from a gas into a liquid on exposed objects like grass, leaves, flowers, and manmade objects like cars and fences. (If it's cold enough, the water droplets can turn into ice, forming frost.) Dew occurs when the water vapor condenses faster than it evaporates. As the air cools, and at a certain barometric pressure, it will eventually reach a temperature where the water vapor condenses into dew. This temperature is called the dew point. When the temperature increases during daylight hours, the dew evaporates.

Is it possible to "capture" dew? Yes! In fact, some plants collect the dew that gathers on their leaves and use it to grow. Humans, like plants, have collected dew for hundreds of years in dew traps, shallow holes lined with material that funnels the droplets to the center. The collected water is used to quench the thirst of peoples' animals and plants. In the Canary Islands, a Spanish group of islands that receive less than 10 inches of precipitation per year, farmers planted their vines in holes in the ground. Placed in the center of the hole, the vines' leaves and stems gathered the dew and watered themselves. Medieval English farmers used dew traps to water their animals. They dug holes in the ground, lined them with hay and then clay, and smoothed the clay surface. The hay isolated the clay from the ground. Once the clay hardened, the farmers lined the holes with rocks, which prevented livestock from trampling and damaging the smooth clay surface. The dew condensed on the smooth surface of the clay and then collected at the bottom of the hole. Present-day survivalists also use similar methods to collect water using a limited number of materials. In this project, we will use holes in the ground to function as traps for dew and other water that condenses in the trap.

In this environmental engineering science project, you will build a dew trap to collect water and determine how the surface area of the trap contributes to the amount of water it collects. In this case, the trap will not strictly harvest dew, but the water that condenses on the inside of the cool trap covering. To build the dew trap, you will dig holes 1 foot (ft.) deep (of two opening sizes) in the ground, place a collector at the bottom of the hole, and then cover the hole with clear plastic. Is it possible to collect water this way? How does the size of the hole opening contribute to the amount of water collected?

Terms and Concepts

  • Desert
  • Precipitation
  • Semi-arid
  • Water vapor
  • Humidity
  • Evaporation
  • Transpiration
  • Dew
  • Condensation
  • Frost
  • Barometric pressure
  • Dew point
  • Dew trap
  • Survivalist
  • Diameter
  • Condensate
  • Efficiency

Questions

  • What is the definition of "dew point"? What is the dew point presently where you live?
  • Find examples of plants that collect water from dew. What characteristics do these plants have that enable them to harvest dew? What are the most common characteristics? Do some plants have unique characteristics?
  • What was the purpose of the layer of hay that the Medieval English farmers used to line their dew traps? Would the dew trap have worked without the hay layer?
  • Aside from making a dew trap, what are some other methods for collecting water from thin air?

Bibliography

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Materials and Equipment

  • Trenching shovel
  • Adult volunteer (optional)
  • Collector (2). The collectors can be aluminum pie plates, pans, or food storage containers that cover the majority of the area at the bottom of the hole. Both collectors must be identical.
  • Plastic drop cloth, clear, 2-millimeters thick, 9 X 12 feet (ft.) (1). You can purchase a plastic drop cloth at a hardware store.
  • Scissors
  • Ruler
  • Bricks (10-15), Optional
  • Rocks, egg-size (2)
  • Disposable cups, (6)
  • Cheesecloth, (1 pkg.). You can purchase a cheesecloth from your grocery store or from Amazon.
  • Rubber band
  • Graduated cylinder, 50 milliliters (mL)(1). You can purchase a 50 mL graduated cylinder from Amazon.
  • Lab notebook
  • Graph paper

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Experimental Procedure

Building the Dew Trap

  1. Find an area in your backyard, or in another outdoor place that will not be disturbed by other people, where you can dig two small, round holes.
    1. The area should be in a sunny location away from foot traffic.
    2. Seek permission to dig in the area before you start digging the holes.
  2. You will dig two round holes. If necessary, ask an adult volunteer for help in digging the holes. You can also read this How to Dig a Hole webpage to learn how to dig holes.
    1. The first round hole must have a diameter of 1 foot (ft.) and a depth of 1 ft.
    2. The second round hole must have a diameter of 2 ft. and a depth of 1 ft.
  3. As you dig the holes, place the excess dirt to the side. You will need it to construct the traps.
    1. Make the bottom of the holes flat so that you can easily place a collector at the bottom. You will want the flat bottom area to be large enough so that your collector fits there.
    2. Use the ruler to confirm that the holes are 1 ft. deep each. Figure 1 shows a prepared hole 2ft. in diameter.
Environmental Engineering science project This hole is 1 ft. deep and 2 ft, in diameter.
Figure 1. This hole is 1 ft. deep and 2 ft. in diameter.
  1. Once the holes are complete, center a collector at the bottom of each hole. The collector should cover most of the area at the bottom of the hole.
    1. The collectors must be identical. If they are not, you will be adding another, uncontrolled variable.
  2. Open and spread out the plastic drop cloth. Using the scissors, carefully cut two circles of plastic, one for each of the holes. You will be using the extra plastic to make additional covers. Be sure to position the circles carefully so that you get as many covers of both sizes as possible.
    1. The plastic must be larger than the hole. Specifically, the plastic for the smaller hole should be 4 ft. in diameter and the plastic for the larger hole should be 5 ft. in diameter.
  3. Carefully center each piece of plastic over its hole. Avoid getting dirt in the collector.
    1. Hold each piece of plastic in place with two or three bricks along the circumference of the hole or by piling the excess dirt around the edges.
  4. Gently push each cover down into a cone so that the tip of the plastic is positioned a few inches above the collector at the bottom of the hole. As the condensate, or dew, forms, it will run down the inside of the plastic cover and fall into the collector.
    1. Remove any excess dirt that falls on top of the cover. Light needs to get through the plastic to help condensation take place.
    2. Place an egg-sized rock in the tip of the cone. Make sure that the rock is centered directly over the collector. The purpose of the rock is to stabilize the cover and keep the cone shape.
    3. Completely seal the edges of the plastic cover with more dirt. If the plastic is not sealed, the water can evaporate from the trap.
    4. Check to make sure that the insides of the plastic cover are not touching any part of the rim of the container, since this would prevent some water from being collected.
    5. Figure 2 shows a rectangular-shaped dew trap.
Environmental Engineering science project This figure shows a finished dew trap.
Figure 2. This figure shows a finished dew trap. Notice that the collector, an aluminum-roasting pan, covers most of the area at the bottom of the hole and that a small rock on the other side of the covering helps keep the cone shape. Bricks and dirt from digging the hole keep the covering firmly in place.
  1. The traps are complete. Write down the size of each trap and the start dates and times in your lab notebook in a table like the one shown below.
Hole Trial Start Date
Start Time
End Date
End Time
Amount of Water Collected (milliliters)
Small
(1 ft. diameter)
1   
2   
3   
Large
(2 ft. diameter)
1   
2   
3   
Table 1. Collected water data

Testing the Dew Trap

  1. Allow the dew traps to collect water for three to four days. During this time, monitor the conditions of the dew traps.
    1. Don't allow too much dirt to fall on the cover, make sure that the trap stays in its conical shape, and that the egg-shaped rock is in the proper position in the tip of the cone.
    2. If it rains, use a disposable cup to remove any excess water from the cover.
  2. After three to four days, take the plastic cover off of each of the holes. Work on one hole at a time. Take the plastic cover off at approximately the same time of day that you started the experiment.
    1. Remove the rock from the tip of the cover's cone. Carefully push the excess dirt away from the edges of half of the plastic cover. If using bricks, move them off the edges.
    2. Lift half of the plastic away, overlapping the free half on the other half that is still in place.
  3. Remove the collector from each hole, making sure to avoid dumping any excess dirt into the collector. Set the collectors aside, keeping track of which hole each collector came from.
  4. Use two disposable cups to measure the water in each collector.
    1. On the bottom of one cup, write "large", and on the bottom of the second cup, write "small".
    2. Cut two pieces of cheesecloth, fold them in half, and then cover the top of each disposable cup with a folded cloth.
    3. Put a rubber band around the rim of each disposable cup to hold the cheesecloth in place.
    4. Slowly pour the water from each collector into its marked cup. The cheesecloth will filter any large dirt particles out of the water.
    5. Remove the cheesecloth and set the cup aside for an hour. Any dirt suspended in the water will settle at the bottom of the cup.
  5. After an hour, measure the water in the cups.
    1. Slowly pour the water from the cup for the small hole into the graduated cylinder, making sure not to spill any water from the cup outside of the cylinder or pour in any of the dirt that settled at the bottom of the cup. Record the data for the small hole in your lab notebook, noting the end date and the amount of water collected from the small dew trap in Table 1. Discard the water in the graduated cylinder from the small hole cup and repeat the measurement with the large hole cup, recording how much water it contains. Record this data in Table 1 as well. Don't drink or taste any of this water, as it may contain chemicals and dirt.

Repeating the Experiment

  1. Replace the covering on both the large and small holes with new sheets of plastic circles and repeat the experiment two more times, waiting the same amount of time to collect water for each trial, for a total of three trials.
    1. It is important to redo the experiment two more times to ensure that the data is reproducible and accurate.
    2. Record the data in Table 1 of your lab notebook, making sure to identify each set of data by its trial number.

Analyzing Your Data

  1. Review the data in Table 1. Average the data for each of the holes over the three trials. Record the average data in a table like Table 2 shown below.
    1. Calculate the approximate opening area of each hole (in feet squared) and record it in Table 2. Equation 1 shows how to calculate the area of a circle (or top surface of the dew trap).

      Equation 1:
      Area = Πr2
      • Π = 3.1415
      • r = radius of the top surface of the dew trap

    2. Divide the average amount of water collected (in milliliters) by the approximate area of the hole (in feet) to calculate the average amount of water collected per area (in milliliters per square foot) for each hole. Record this data in Table 2.
Hole Average
Amount of Water Collected
(milliliters)
Approximate
Area of the Hole
(feet squared)
Average
Amount of Water
Collected per Area
(milliliters/feet squared)
Small
(1 ft. diameter)
   
Large
(2 ft. diameter)
   
Table 2. Average collected water data
  1. Plot the data from Table 1 for each trial.
    1. Label the x-axis Approximate Area of the Hole (feet squared) and use the values you calculated for Table 2. Label the y-axis Collected Water (milliliters) and use the data from Table 1. Were there many differences between the three trials?
    2. If you would like to plot your data online or need additional information on graphing, go to the Create a Graph website for more information.
  2. Plot two graphs using the data from Table 2.
    1. For the first graph, label the x-axis Approximate Area of the Hole (feet squared) and label the y-axis Average Collected Water (milliliters). Were the average collected water values similar to the values in the graph from step 2?
    2. For the second graph, label the x-axis Approximate Area of the Hole (feet squared) and label the y-axis Average Amount of Water Collected per Area (milliliters/feet squared). This graph compares the efficiency of the dew traps. Did one of the holes have a higher efficiency than the other? Did a particular trap collect more water per square foot, or were the amounts of water collected per square foot similar for each hole? If there are differences, why do you think they exist?
  3. How does the size of the trap affect the amount of water collected? Do you think that this is a viable method for collecting water? Why or why not?

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Variations

  • How does the amount of sunlight the trap receives affect the amount of water it collects? If you place the trap in a shady location, will it still collect water? Will the amount of water be comparable to the amount of water from the trap in the sunny location?
  • Try making dew traps out of different materials and using slightly different designs. You may want to read more about how different dew traps are made. Can you design a dew trap that is more efficient than the one used in this experiment? What are the most important features for improving its efficiency?
  • If you live in a foggy area you can build a fog trap to collect water from the air. This article from CNN relates how farmers in Peru are capturing water for part of the year from fog. They can harvest enough water this way to sustain agriculture. Try building your own fog trap. How much water can you collect with your trap?
  • Test the water to see how clean it is. How clear is it? Is this water safe to drink?
  • Humans require 9 to 13 cups of water each day for good health. How many traps would you need to build in order to have enough water to drink for the day? How many would you need to get enough water for your family?

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