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Solar-Powered Water Desalination

Difficulty
Time Required Average (6-10 days)
Prerequisites None
Material Availability Some specialty items needed, see Materials list for details. For your convenience a Science Buddies Kit is available for purchase.
Cost Average ($50 - $100)
Safety A hand drill is needed for some steps. Adult assistance is needed for the steps involving a hand drill. All items in the Science Buddies Kit come pre-drilled, eliminating this safety issue.

Abstract

How can seawater from the oceans be turned into fresh water that is suitable for people to drink? Through a process called solar desalination! In this science project, you will make a solar desalination apparatus using readily available materials, and a power source that is free. How much water can the device produce, and is it still salty at all? What factors affect how effectively saltwater is turned into fresh water?

Objective

Build and test a solar-powered device for desalinating water and investigate how the color of the bottom of the device affects its efficiency.

Credits

Andrew Olson, Ph.D., and Teisha Rowland, Ph.D. Science Buddies

Sources

This project is based on the following 2007 California State Science fair project, a winner of the Science Buddies Clever Scientist Award

Cite This Page

MLA Style

Science Buddies Staff. "Solar-Powered Water Desalination" Science Buddies. Science Buddies, 6 Oct. 2014. Web. 25 Oct. 2014 <http://www.sciencebuddies.org/science-fair-projects/project_ideas/EnvEng_p022.shtml?from=Blog>

APA Style

Science Buddies Staff. (2014, October 6). Solar-Powered Water Desalination. Retrieved October 25, 2014 from http://www.sciencebuddies.org/science-fair-projects/project_ideas/EnvEng_p022.shtml?from=Blog

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Last edit date: 2014-10-06

Introduction

Nicholas Kinsman is interested in inventing solar-powered devices to reduce our dependence on other energy sources. He is also a winner of a Science Buddies Clever Scientist award for his 2007 California State Science Fair project (Kinsman, 2007). Nicholas set out to build a simple, inexpensive device to desalinate seawater, using readily available materials and easy construction methods.

Typical seawater contains dissolved salts at concentrations between 32 and 37.5 parts per thousand. That means that if you started with one kilogram of seawater (which is approximately one liter of seawater) and then you allowed all of the water to evaporate, you would be left with between 32 and 37.5 grams of salts (also called "total dissolved solids").

With all of that salt, seawater is not suitable for drinking nor for watering most plants. The fluid circulating in your body (blood plasma) contains much less salt than seawater (on the order of 9 grams of total dissolved solids). If you were to drink seawater, your body would actually lose water, because the high salt concentration of the seawater causes an osmotic pressure gradient which drives water out of your cells. Desalination is the process of removing the dissolved salts from water, making it pure enough for drinking or irrigation.

Nicholas's first design for a desalination device is shown in Figure 1 below. There are eight small bottles surrounding the large collection jug. Each of the small bottles is filled with seawater. The small bottles have holes in their caps. One end of a flexible straw is inserted into the hole, and the other connects to the large collection jug at the center. When the entire device is set out in the sunlight, the seawater in the small bottles heats up, which causes the water to evaporate and fill the small bottles with water vapor. The idea was that as the water vapor increased, it would condense in the straws and flow down into the collection jug. Unfortunately, the idea did not work. You can see in the picture that there is condensation on the inside of the top of the bottles, but there was very little condensation in the straws.

desalination device, first try
Environmental Engineering science project

Figure 1. This is Nicholas's first try at a solar-powered desalination device. The idea was to add saltwater to the eight small bottles. The condensation was supposed to drip down from the straws into the large collection jug. Unfortunately, this design did not work. (Photo from Nicholas Kinsman's display board at the fair.)

Like any good inventor, Nicholas did not let an initial setback discourage him. He analyzed what was wrong with the design and set out to improve it. His second design, shown in Figure 2 below, still follows the same principles of using readily available materials and easy construction methods, but also includes some important improvements. One important change is that this time Nicholas's design uses a container with a larger surface area to hold the seawater.

desalination device, first try
Environmental Engineering science project

Figure 2. Here are two examples of Nicholas's second design for a solar-powered desalination device. The large jug, laying on its side, holds the seawater. The top side of the jug has been cut out with a utility knife. Plastic cling wrap seals the top side, and a quarter is used as a weight to make a low point in the center. Beneath that low point, Nicholas placed a collector, made from the top of a small water bottle with a flexible straw inserted into a hole in the cap. The other end of the straw passes through the side of the large jug, and then to a plastic cup where the condensate collects. The device on the left has an aluminum foil reflector covering the back side and bottom of the large jug while the device on the right has no reflector. (Science Buddies photo of Nicholas Kinsman's display board at the fair.)

Why is it important that in the improved design a large jug is used to hold the saltwater? The jug, which is laid on one side, lets the saltwater cover a relatively large area. Because water molecules can only evaporate from the surface of water, a body of water with a large surface area will have a greater rate of evaporation than a body of water with a smaller surface area (assuming all other conditions are the same). The top side of the jug is cut out, using a utility knife, and covered tightly with plastic cling wrap. The cling wrap covering the large opening provides a large surface area on which condensation can form, which is another reason why using a larger container is an important change in this design. A quarter is used as a weight to make a low point at the center of the cling wrap. When the device is heated up in the sunlight, the condensation that forms on the cling wrap eventually flows down to this low point and drips into a "funnel." In Nicholas's design, the funnel is simply the cut-off top of a small water bottle, which has a flexible straw inserted into a hole cut in the cap. The other end of the straw passes through a small hole in the large jug, and then to a plastic cup (tightly covered with cling wrap using a rubber band to prevent evaporation).

For his science fair project, Nicholas tested the desalination devices based on his second, improved design with and without aluminum foil reflectors (you can see examples of each type in Figure 2 above). For each device, he made several measurements so that he could compare the performance, including the amount of condensate collected, or his condensate yield, and the conductivity of the saltwater and condensate. The yield measurements told him how efficient his devices were at heating the saltwater and producing desalinated water. The conductivity measurements (which can be taken using a handheld meter) told him how well the condensed water had been purified of dissolved salt because water that contains dissolved salt can conduct electricity, and the more salt that is dissolved in the water, the higher the conductivity of the water.

In this environmental engineering science project, you will build desalination devices similar to Nicholas's second design and see how the design can be improved even more. Specifically, you will investigate how the color of the bottom of the device affects its efficiency. You will compare a device with a white-colored bottom to a device with a black-colored bottom. Something that is light-colored reflects more light than something that is dark-colored, which absorbs a lot of the light that hits it. Light is a form of energy and energy can be transferred to nearby objects (such as a body of water) in the form of heat, in a process known as heat transfer. Which colored bottom do you think will result in a more efficient desalination device?

Terms and Concepts

  • Solar-powered devices
  • Desalination
  • Water purity
  • Evaporation
  • Water vapor
  • Condensation
  • Surface area
  • Yield
  • Reflection of light
  • Absorption of light
  • Heat transfer

Questions

  • Why does condensation form when water is heated up?
  • What are some factors that affect the rate of evaporation?
  • Do you think a desalination device with a black-colored bottom would be more efficient than one with a white-colored bottom? Why? Can you relate your answer to the concept of heat transfer?

Bibliography

Do further research by visiting the following websites, which give information about salts in seawater, desalination, and rate of evaporation:

This project is based on the following 2007 California State Science fair project, a winner of the Science Buddies Clever Scientist Award:

Materials and Equipment Product Kit Available

The Experimental Procedure shows how to make a water desalination device from plastic shoeboxes rather than the water jugs Nicholas used. You will need these items:

  • Clear plastic shoeboxes (2); alternatively you can use other large clear plastic containers like 1 gallon water jugs. Two of the same kind of container must be used.
    • Tip: Containers with a large surface area, sides that do not lean inwards, no overhang around the top opening, and straight, flat edges around the opening are ideal. If you are using containers without removable lids, like water jugs, you will need a utility knife.
    • The Science Buddies Kit comes with two ideally sized clear plastic shoeboxes. These shoeboxes are pre-drilled. No utility knife or drill is needed.
  • Small funnels (2); alternatively try making your own funnels out of the cut off top of a 1 pint water bottle.
    • The Science Buddies Kit comes with two 5 mL funnels.
  • Hand drill and 5/16" or ¼" drill bit
    • All items come pre-drilled in the Science Buddies Kit. No drill is needed.
  • Flexible plastic straws (2)
  • Scissors
  • Modeling clay (small amount)
  • Tape
  • Optional: Ruler
  • Plastic cling wrap
  • Disposable plastic cups (2)
  • Quarters or metal washers, 7/16 inch size (2)
  • Rubber bands (2); must fit snuggly around the plastic cups.
  • Black construction paper (3 sheets)
  • White construction paper (3 sheets)
  • Water
  • Measuring cups or 100 mL graduated cylinder
  • Beaker or measuring cup large enough to hold 500 mL (1)
  • Salt (50 g)
  • Measuring tablespoon or kitchen scale
  • 25 mL graduated cylinder
  • Clock
  • Lab notebook
  • Access to direct sunlight outside for three days
  • Optional: Outdoor thermometer

Disclaimer: Science Buddies occasionally provides information (such as part numbers, supplier names, and supplier weblinks) to assist our users in locating specialty items for individual projects. The information is provided solely as a convenience to our users. We do our best to make sure that part numbers and descriptions are accurate when first listed. However, since part numbers do change as items are obsoleted or improved, please send us an email if you run across any parts that are no longer available. We also do our best to make sure that any listed supplier provides prompt, courteous service. Science Buddies does participate in affiliate programs with Amazon.comsciencebuddies, Carolina Biological, and AquaPhoenix Education. Proceeds from the affiliate programs help support Science Buddies, a 501( c ) 3 public charity. If you have any comments (positive or negative) related to purchases you've made for science fair projects from recommendations on our site, please let us know. Write to us at scibuddy@sciencebuddies.org.

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Experimental Procedure

Making the Desalination Devices

In this part of the science project, you will make two desalination devices.

  1. If you are using clear plastic shoeboxes, like those in the Science Buddies Kit, skip to step 2. If you are using a water jug, lay it on its side and, using the utility knife, carefully cut out the side that is facing up. Prepare both jugs the same way. If you are using clear plastic containers, skip this step.
    1. Look at Figure 2 in the Background for an idea of what the cut out side should look like. You will want as little jug hanging over the top as possible since any overhanging bottle can trap condensation.
    2. Safety Note: Work carefully when using the utility knife since it will be sharp! Using a new, sharp blade will make the job easier. It is recommended to have an adult help you with this step.
    3. Be careful with your fingers around the cut edges of the jug: they will be sharp!
  2. Look at Figure 3 below to get an overview of what you are making. Take a funnel and connect it to the end of the short side of a bendable straw. Repeat for the second funnel and straw.
    1. If you are using shallow jugs or containers, you may need to shorten this side of the straw so that the funnel does not stick up too far.
      1. You can look at your device setup now and see if you think the straw should be cut, or you can adjust this later (such as in step 8 below).
      2. Science Buddies Kit: If you are using the kit for this project idea, the short end of the straw should be cut with scissors so there is just enough length straw left for the end of the funnel to fit in (or about 1 centimeter [cm] or less above the bendable part). If you do not want to cut too much off, you can skip cutting the straw for now and do it later (such as in step 8 below).
    2. Fit the funnel inside the end of the straw and push the funnel in as far as it will go. Then securely tape the straw to the funnel.
  3. Use the hand drill to make a hole near the bottom of one side of each container for the straw to go through. Skip this step if you are using the Science Buddies Kit; all holes are pre-drilled in the science kit.
    1. Center the hole along one side and make it very low on that side, approximately 2 cm up from the bottom of the container. The hole should be just above where the water level will be. If the hole is too high then the funnel might not be low enough to collect condensation.
    2. Make the hole in the same position on both containers.
  4. Put a straw-funnel assembly through the bottom hole of each container so that the funnels are on the inside of the containers. Adjust the straw-funnel assemblies so that the funnels face up. Put some modeling clay around the hole, on the outside of the jug or container, to hold the funnel in place. Your setup should now look similar to Figure 3 below.
    1. Do not worry if the funnel will not stay in place. The following steps will help secure it.


Straw-funnel assembly in container.
Environmental Engineering science project

Figure 3. After putting the straw-funnel assembly in the hole in the container and securing it using some modeling clay, your setup should look similar to the one shown here. The top picture shows a close-up from the side and the bottom picture shows an overall view from above.

  1. Next prepare the collection cups by drilling a hole near the bottom of each disposable plastic cup. Skip this step if you are using the Science Buddies Kit; the science kit comes with pre-drilled holes.
    1. Make the holes lower than the holes in the containers so that the straws slope down towards the collection cups. For example, if you made the holes in the containers about 2 cm up from the bottom, make the holes in the collection cups about 1.3 cm up from the bottom.
    2. Carefully use a hand drill and drill bit to make a hole in each cup just large enough for the straw to fit through.
  2. Put the empty end of each straw through the hole in a collection cup. If needed, adjust the straw so that the funnel faces up. Put some modeling clay around each hole, on the outside of each collection cup, to keep each cup in place.
    1. Do not worry if a cup is tilted so that it is not completely sitting flat.
    2. If the straw is too long for the funnel to face up and the straw to slope down towards the collection cup, cut a little bit of the straw off and test the setup again. Keep cutting a little bit of the straw off and retesting the setup until it works.
    3. Science Buddies Kit: If you are using the kit for this project idea, cut the straw so that the long end is about 10 cm (or less) long after the bendable part.
  3. Cover the openings on each jug or container with plastic cling wrap.
    1. Tear off two pieces of cling wrap, each large enough to completely fit over the opening in the containers and have some extra cling wrap on the sides.
    2. Tightly put one piece of cling wrap over each opening. Tape the cling wrap to each of the four corners of the container (using only one or two pieces of tape per corner).
  4. Set a washer or quarter on the middle of the cling wrap, right above the funnel. Do this for each desalination device. Adjust the different components so that the washer or quarter creates a low point in the cling wrap right above the funnel, but make sure it is not so low that the cling wrap touches the funnel. For an example of this, see Figure 4 below.
    1. If the cling wrap is touching the funnel, not all of the condensation will go down into the funnel. To fix this, either lower the funnel (such as by cutting the straw) or raise the cling wrap (by taping it tighter).
    2. If you need to drill a new hole to lower the funnel, plug up the old hole with some modeling clay.
    3. If the cling wrap is so tight that it does not form a low point where the washer or quarter is, un-tape it in places and re-tape it more loosely.


Desalination device partly assembled.
Environmental Engineering science project

Figure 4. Place the washer or quarter on the cling wrap, right above the funnel. Make sure that the cling wrap is not so low that it is touching the funnel. The top left picture shows the entire setup at this point. The top right picture shows a close-up of the collection cup and washer. The bottom picture shows a close-up of just the washer and funnel.

  1. After you are done adjusting your setup, cover each collection cup with cling wrap and secure the cling wrap tightly with a rubber band, as shown in Figure 5 below. This prevents your desalinated water from evaporating.
    1. Make sure that there are no gaps or holes in the cling wrap.


Condensate collection system.
Environmental Engineering science project

Figure 5. Secure a piece of cling wrap on to the top of each collection cup using a rubber band, as shown here.

  1. Cover the outside bottom of one desalination container with black construction paper and cover the other one with white construction paper.
    1. Arrange the construction paper so that it goes up about 2 to 3 cm on the sides of each jug or container.
      1. You may need to cut a small slit in the construction paper for the straw to get through.
    2. Note: If you have a large container, such as the one in the Science Buddies Kit for this project idea, you will need to tape two pieces of construction paper together for each jug or container. If you end up with extra paper when you do this, cut it off (instead of letting it overlap) and save it in case the paper gets damp and you want to replace it.
    3. Tape the construction paper in place on the outside bottom of each desalination container.
  2. Make up a single batch of saltwater for both desalination containers.
    1. You will want to fill each jug or container with enough saltwater to just barely cover the bottom. You can determine how much saltwater you will need to do this by filling the jug or container up with a little tap water at a time from a measuring cup or graduated cylinder, and keeping track of how much water you have added. If you do this, dry out the jug or container afterwards.
    2. Once you know how much saltwater you will need, you can make it up in a large cup or bottle. For each 500 mL of water, add 17.5 grams (about 1 tablespoon) of salt. Mix the salt so that it dissolves in the water.
    3. Science Buddies Kit: If you are using the kit add 1 tablespoon of salt to the tripour beaker and fill it to the 500 mL mark. Mix with a spoon until the salt is dissolved. Each of the desalination containers will need 250 mL of saltwater.
  3. For each desalination container, remove the washer or quarter, gently remove the tape on one corner, lift the cling wrap, and pour in the saltwater. Add enough so that it just barely covers the bottom of the container.
    1. Science Buddies Kit: If you are using the kit, pour 250 mL of saltwater into each desalination container.
    2. Make sure to add the same amount of saltwater to both jugs or containers.
    3. Be careful not to let any saltwater spill into the funnel or onto the construction paper.
  4. Put the cling wrap back in place, making sure it is taped on all four corners of each container.
  5. Your desalination devices should look similar to the ones in Figure 6 below. They are now ready for testing!


Complete desalination device.
Environmental Engineering science project

Figure 6. When your desalination devices are ready for testing, they should look similar to the one in the top picture (except yours should have black or white construction paper on the bottom). The diagram on the bottom shows what the desalination devices should look like during testing as condensation is collected. (The construction paper is not shown in the diagram.)

Testing the Desalination Devices

In this part of the science project, you will test the performance of the desalination devices.

  1. Carefully take the desalination devices outside to an area that will receive direct sunlight for at least four hours.
  2. Prepare your desalination devices for testing and do a final check to make sure that everything is in place and ready.
    1. Make sure the cling wrap is taped to all four corners of each container.
    2. Set a washer or quarter in the middle of the cling wrap of each device.
    3. Tape the cling wrap on the sides of the jug or container, using only one or two pieces of tape per side.The cling wrap should now completely seal the large opening on the top of the jug or container. If it does not, water vapor may escape.
    4. Try to get rid of any large wrinkles that do not flow down to the washer or quarter. Wrinkles can prevent the condensation from smoothly rolling down to the collection point.
    5. Make sure that the washer or quarter is at the lowest point of the cling wrap. If it is not, un-tape, adjust, and re-tape the cling wrap to fix this.
    6. Make sure that the funnel is facing up, directly below the washer or quarter, and not so high that it is touching the cling wrap. If the funnel is touching the cling wrap, either lower the funnel or raise the cling wrap by taping it higher.
    7. Make sure that the modeling clay has sealed the holes to prevent evaporative losses. Add extra modeling clay if needed.
    8. Check that the straws slope down towards the collection cups. Even a mild slope is enough to work.
  3. In your lab notebook, record the time.
    1. Optional: measure and record the temperature near the desalination devices. You can use this information later to determine how temperature affects the condensation yield.
  4. Check on the desalination devices after about 30 minutes. You may see condensation starting to form small drops on the cling wrap right below the washer or quarter. However, it may take longer, depending on how sunny and warm it is.
    1. If you see condensation forming small drops, do you see it on both desalination devices, or only one of them? Record your observations in your lab notebook.
    2. If needed, adjust the washer or quarter and funnel-straw assembly on each device to make sure that the drops fall into the funnel.
      1. You can arrange the washer or quarter so that one edge of it is the lowest point on the cling wrap, and this edge is positioned over the funnel so that condensation drips into it, as shown in Figure 7 below.


Condensation collecting below the washer, above the funnel.
Environmental Engineering science project

Figure 7. As shown in this close-up picture, you can arrange the washer so that its edge is the lowest point on the cling wrap and is positioned over the funnel, allowing condensation to drop into it.

  1. Continue checking on your desalination devices every 30 minutes to make sure that they are still in the sunlight and that the condensation drops are falling into the funnel.
    1. If the desalination devices are not in the sun, gently move them to a sunny location.
    2. Does it look like one desalination device is making more condensation drops than the other? Record your observations in your lab notebook.
    3. If it is warm enough, the modeling clay may melt a little. If it does, just make sure that the holes are still sealed by the modeling clay. Add more clay if needed.
    4. If it is windy, you may want to check on your desalination devices more frequently to ensure that everything is still in place and functioning properly.
  2. Stop your testing after your desalination devices have been in the sunlight for at least four hours.
    1. In your lab notebook, record the time when you stop your testing. How long were your desalination devices in the sunlight?
    2. Optional: again, measure and record the temperature near the desalination devices.
  3. Open the large cling wrap covering on each device and try to get any condensate that is still in the straw to go out and into the collection cup. You can do this by gently blowing into the straw.
  4. To determine the condensate yield of each desalination device, carefully disconnect the collection cup, remove its cling wrap covering, and pour the collected condensate into the 25 mL graduated cylinder.
    1. What was the condensate yield of each device? Record your results in your lab notebook.
  5. To determine whether the collected condensate is still salty, taste a little bit from each device. Record your observations in your lab notebook.
  6. Repeat this experiment at least two more times on different days for a total of three trials. This will help ensure that your results are consistent and reproducible.
    1. Between trials, carefully rinse out each desalination device with tap water and let them dry along with all of the other desalination device components.
    2. When you are ready to repeat your testing, fill the desalination devices with saltwater as you did in step 11 - 12 of "Making the Desalination Devices."
      1. Use the same amount of saltwater in each device and trial.
    3. Repeat the rest of the testing as you did in steps 1-9 of "Testing the Desalination Devices." For each trial, perform the testing for the same length of time.
  7. After you have tested both devices in three trials, make a bar graph of your condensate yield results.
    1. On the x-axis of the graph, list your desalination devices. You can average the results for each device for the three trials, or you can show all three trials separately.
    2. On the y-axis, put the condensate yield in milliliters.
  8. Analyze your results.
    1. Did one desalination device consistently have a higher condensate yield than the other? If so, why do you think this is? What does this tell you about the features an effective solar desalination device should have?
    2. Was the collected condensate ever salty?
    3. If you measured the temperature near the desalination devices during testing and the temperature varied a lot between your three trials, do you see a correlation between the temperature and the condensate yield?
  9. Taking 3 liters as the minimum required amount of drinking water per person per day (NAS, 2004), how many devices would you need to produce enough water for your survival needs?
    1. You can divide the condensate yield by the testing time to get an average collection rate (mL/hour). You will need to think about how many hours of sunlight there are in your area. Would it change with the season?

Troubleshooting

For troubleshooting tips, please read our FAQ: Solar-Powered Water Desalination.

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Variations

  • In this science project you compared the performance of desalination devices with a black-colored bottom and a white-colored bottom. What do you think would happen if you used an aluminum foil reflector, as Nicholas Kinsman did (as discussed in the Background)? How do you think you could set up such a reflector so that it heats up the water in the device as much as possible? Hint: research parabolic reflectors.
  • How does the temperature of saltwater affect the rate of evaporation? You can try this science project again but this time fill one desalination device with ice-cold water and the other with hot water. Is one device much more efficient than the other?
  • Surface area is a factor that affects the rate of evaporation. Think of a way to modify one of your desalination devices so that the same volume of saltwater takes up only half of the surface area of the bottom of the jug or container, such as by attaching a plastic divider to the bottom. Test the two desalination devices again, using the same volume of saltwater in each. Does the change in surface area correlate with a change in condensate yield?
  • Saltwater has a higher boiling point than freshwater. Does this mean that you would get a higher condensation yield using freshwater than you did using saltwater? To find out, you can try this science project again but this time use saltwater in one desalination device and freshwater in the other. To make sure you are collecting "pure" water, you can add some food coloring to the initial water in each device. Are the condensate yields very different between the two devices? If you try even saltier saltwater than was used in this science project, is there a greater difference?
  • How does the collection rate change during the course of the day? To investigate this, it would be a good idea to have your collection container marked with graduated volumes. That way you can measure collection volumes easily without disturbing the collection system.
  • In what other ways do you think you could change your desalination device to improve its efficiency? Find out what factors affect the rate of evaporation and how other desalination devices are designed. Figure out how you can use this information to modify your device, or design a completely new device, to improve efficiency.
  • You can build other useful devices that use solar power. For example, the Science Buddies project Now You're Cooking! Building a Simple Solar Oven shows how to build a solar oven. Can you adapt a solar oven to make a solar-powered desalination device? Is it more or less efficient than the plastic bottle desalination device from this project?

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Frequently Asked Questions (FAQ)

If you are having trouble with this project, please read the FAQ below. You may find the answer to your question.
Q: I think I am having low yields. What yields should I expect and what are some things I can do to improve my yields?
A: If you are using the Science Buddies kit for this project idea, the setup should yield at least 8 milliliters (mL), but depending on the weather conditions and other factors it may yield significantly more. There are a number of factors that can affect the yield in this science project. Here are some things to check:
  • Make sure there are no large wrinkles in the plastic cling wrap, as this can trap condensation. To get rid of a large wrinkle, try taping up a little more cling wrap in that area. Also make sure that the corners and sides of the jug or container are taped to the cling wrap. The cling wrap should allow condensation to roll smoothly down to the collection point, below the washer or quarter.
  • If you are using funnels made from the tops of 500 mL plastic water bottles, make sure that condensate is not pooling and getting trapped in the funnel. Make sure the straw is not sticking into the funnel, but is flush with the cap. You may want to try small, pre-made funnels as an alternative.
  • You can try filling the jug or container with less salt water. You should fill it with enough to just barely completely cover the bottom of the jug or container, but do not add any extra salt water. All of the water needs to be heated up enough for water to start evaporating, so if you use more water then more energy will be required to heat it up.
  • Watch to make sure that the condensation is actually dripping directly into the funnel, and make adjustments to the position of the funnel and washer or quarter if it is not.
  • Make sure that all holes are sealed using modeling clay. If it gets very warm, the modeling clay may melt, so make sure that there is enough modeling clay that even if a little melts it is still sealing the holes.
  • This science project will work best when it is warm and done in direct sunlight, so try to avoid testing it when it is cool and/or overcast.
  • If you are not using the Science Buddies kit, selecting the right jug or container is important. Use a jug or container with a large surface area, since water molecules can only evaporate from the surface of water. It is recommended to use a jug or container with at least 1500 cm² of flat surface area on the bottom. Make sure the jug or container has straight sides that do not lean inwards and has no overhangs, as these features can trap condensation.
Q: Why is it important that I make the hole in the jug or container near the bottom of the container?
A: If the hole it too high, the funnel may touch the plastic cling wrap, which can prevent some condensation from dripping into the funnel and result in lower yields. The hole should ideally be placed as low as possible, just above the water level in the jug or container. The hole in the collection cup should be lower so that the straw slopes down towards the collection cup.
Q: The funnel keeps tilting so that it does not completely face up. What should I do to fix this?
A: If the funnel is tilted a little it should still work fine, as long as you can see that the condensation drips directly into the funnel.
  • If you need to change where the condensation is collecting, you can move the washer or quarter and/or adjust the saran wrap (by taping or re-taping it). You may need to move the washer or quarter so that the condensation collects along one edge, and position this edge over the funnel, as shown in Figure 7 in the project idea.
  • Without taking apart your setup, you can try adjusting the position and angle of the funnel by moving the part of straw that is between the jug or container and the collection cup, or by moving the collection cup.
  • The collection cup does not need to sit completely flat to function, but if it is windy and the collection cup is being knocked over, you can tape it to the jug or container.
  • If the funnel seems too heavy to stay upright, try using a long, thin piece of tape to tape the funnel (on the outside rim) to the inside top edge of the jug or container to keep it upright. If you do this, a little condensation will be lost on the tape, but it will be much better than having a funnel that does not work.
Q: My results are not what I expected them to be. Why might this be?
A: If different amounts of salt water were added to each jug or container at the beginning of the experiment, or the salt water added was a different temperature in each one, this could affect how well the water evaporated in each one. All factors should be the same for each jug or container, except the color of the construction paper. You may also want to make sure that the condensation is dripping directly into the funnel for each setup, and make adjustments to the setup if it is not.
Q: My washer or quarter is bigger than the funnel. Is this a problem?
A: No, you should be able to move the washer or quarter so that the condensation collects right beneath one edge of the washer or quarter. Position this edge over the funnel and watch to make sure that the condensation drips directly into the funnel, as shown in Figure 7 in the project idea. Make further adjustments to the setup if needed.

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