Offgrid / Outdoor Tips
"Catch Water from the Air"
How long do you think you could survive without drinking any water? Only three to four days! Your body needs water to function properly. We also rely on water for cooking, cleaning and many other activities. You might not think about getting enough water if you live in an area where you can get it easily by turning on your faucet. But what about areas that don't have a reliable water supply? In this activity you will learn about one creative way to collect water—from the air!
Many people around the world struggle to have enough fresh water for daily necessities. Because of that, people have gotten creative in finding other ways of getting the fresh water they need. For example, people who live near the coast sometimes collect water by harvesting it from fog!
Fog is a low-hanging cloud that touches the ground. The air around us contains moisture in the form of water vapor. Usually a cloud (or fog) forms when the air temperature gets cool enough that the water in the air starts to condense, which means that the water vapor turns into tiny water droplets in the air. The collection of these tiny water droplets make a cloud (or fog) visible to us. In the case of fog they can even make it difficult to see very far.
Coastal regions frequently get fog because the warm air of the land meets the cooler air from the ocean—right around or just above ground level. When these air layers collide, the water vapors condense and fog is created.
But how can you get water out of the fog? You have to find a way to collect the tiny water droplets out of the air. This is done with big meshes that are set up perpendicular to the path of the wind. As the wind carries the fog through these meshes the water droplets get caught by the mesh. Once the droplets accumulate and become big enough, gravity pulls them down the mesh and into containers that are set up to collect the water. In this activity you will build your own fog catcher and harvest water from the air—with simulated fog.
Materials
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Work area that can get wet
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Pantyhose
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Wire coat hanger
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Tape
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Clear drinking glass, cup or jar
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Modeling clay
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Refillable spray bottle
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Water
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Paper
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Pen or pencil
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Scale (optional)
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Second glass, cup or jar (optional)
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Measuring cup (optional)
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Humidifier (optional)
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Various other mesh materials (optional)
Preparation
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Take the wire coat hanger and form it into a diamond shape by stretching it out.
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Place one end of the pantyhose over the diamond-shaped hanger and secure it at the bottom with tape.
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Place a large lump of modeling clay at the bottom of your clear glass, cup or jar.
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Straighten the hook of the wire coat hanger.
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Place the straightened hook into the clay so it stands upright and is stable.
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If you're using a scale, you can weigh your fog catcher, and write down the weight.
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Fill the spray bottle with tap water.
Procedure
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Take the spray bottle, and point it away from your fog catcher. Squeeze the trigger until it starts spraying. What can you see when the bottle starts spraying?
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Now hold the spray bottle about a foot away from—and perpendicular to—the net of your fog catcher. Aim the spray bottle at the fog catcher, and pump it about 10 times. Inspect the mesh afterwards. What do you see?
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Spray the net with water another 10 times. What do you observe now?
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Repeat this step about 10 times. After every 10 sprays inspect the mesh of your fog catcher. How does the surface of your net change every time?
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What do you see in the bottom of your collection container? If you used a scale, you can place the whole fog catcher onto the scale again, and write down its mass. Did the mass of the device change? If yes, how? Can you explain the change?
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Extra: Spray your sprayer directly into another glass, cup or jar the same number of times you sprayed it onto your fog catcher. Compare the amount of water in each container or measure them in a measuring cup. How efficient was your fog catcher at capturing the water available?
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Extra: Instead of using a spray bottle you can also place the fog catcher close to a humidifier. How does this change your results?
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Extra: Try out other mesh materials that you have in your house. What are the best materials to catch water from the air? You can measure the fog catching efficiency by measuring the weight of the fog catcher before and after spraying it with water. In order to compare your results you will need to use the same amount of water for each material you test.
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Extra: Does it matter how you hold the spray bottle in front of the fog catcher? How does the distance or angle at which you are directing the mist towards the mesh affect the efficiency of the fog catcher?
Observations and Results
The device that you built from the pantyhose and coat hanger is a simple model of a fog catcher, which usually consists of a mesh stretched across a frame and a collection container below it. You used the spray bottle to mimic the fog. The nozzle inside the spray bottle breaks the stream of water into many tiny water droplets. You can see these water droplets coming out of the spray bottle. These droplets mimic fog, which is also small water droplets dispersed in the air.
When these water droplets passed through the fog catcher they were collected by the mesh. You probably didn't see much after 10 sprays, but after a while, you should have seen tiny little water droplets building up on the surface of the pantyhose. The more fog the mesh had collected, the more water droplets accumulated. At some point they probably started to merge and formed bigger drops that then ran down the surface into the container—thanks to gravity. You could probably start to see the water pooling in the bottom of your container. If you used a scale, you could weigh the difference between the device at the beginning of the activity and at the end, which reflects the amount of water you collected from the air!
If you tried different meshes, you might have collected different amounts of water. Scientists are still trying to optimize the materials and designs of fog catchers so they can be even more efficient in water harvesting. In real-life fog catchers, depending on the mesh material and design, they can harvest as much as nine liters of water per day for each square meter of mesh.
Cleanup
If the pantyhose are still intact after the activity, you can dry and reuse them. You can also reshape the wire hanger into hanger form, and reuse it as well.
Source ~ Scientific American