Photo of supplies and two steps for the Water Cycle in a Bag project.
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Water Cycle in a Bag

Emily from the SMO programs team loves rain and knows it’s just one step on a larger process called the water cycle! The water cycle is the path water follows as it moves from the surface of the earth up into the atmosphere and back to the ground again. 

Photo of the supplies for making cloud in a bag and a photo of two steps.

Emily from the SMO programs team loves rain and knows it’s just one step on a larger process called the water cycle! The water cycle is the path water follows as it moves from the surface of the earth up into the atmosphere and back to the ground again. 

There are four steps to the water cycle. You probably know them or have heard of them: 

Let’s start with evaporation. During evaporation, heat from the sun cases water to turn to a gas called water vapor. This gas rises into the atmosphere. As the water rises higher into the air, it cools down and turns back down and forms clouds. We call this cloud-forming step condensation

When the clouds become too saturated with water and the water becomes too big and heavy for the air to hold up any longer, gravity will pull that water to the ground in a step called precipitation

Rain, hail, sleet, drizzle, and even snow are all forms of precipitation. After the rain, or other form of precipitation falls to the ground, it collects in ground, ponds, lakes, rivers, oceans and other bodies of water. You guessed it, this step of the water cycle is called collection

These four steps then repeat in the water cycle — and with just a window, some water, and a resealable bag, you can create your own water cycle!

Here’s what you need:

  • A window, preferably one that receives some rays from the sun
  • A resealable plastic bag, a quart size bag is a great size
  • 1/4 cup of water
  • Tape, really sticky stuff that can secure your bag to a window 
  • Marker (this is optional but helps a lot)
  • Food coloring, this is also optional but food coloring does make things cooler

 

Here’s what to do:

1. If you have a marker, draw the water cycle on the outside of your bag. The part of the bag that opens and closes should be the top of your drawing. Though this step is optional, it does help visualize what is going on. If you need a model of the water cycle, check out Emily’s video.

2. Pour 1/4 cup of water into your bag. You can add a couple of drops of food coloring if you got them. With water pooled at the bottom of your bag, what step of the water cycle would this be?

3. Hang your bag on a window using the tape. Try to select a place that gets direct sunlight!

3. Leave your bag on the window for an hour.

4. After an hour, check back on the bag. What do you notice? Does there appear to be less water gathered at the bottom of the bag? What could cause this? Does it appear foggy in the bag? Do you detect any signs of condensation?

5. Keep monitoring the bag and making observations. What happens when water droplets form on the bag? Are the droplets big or tiny? What would happen if they got very big?

Through your observations, see if you can observe all four stages of the water cycle. There are lots of ways to further experiment with this exploration. 

  • Instead of using the heat from the sun, could you use an incandescent lightbulb? 
  • Would evaporation begin sooner if you started with warm or cool water? 
  • Does fresh or salt water evaporate faster? 
  • What would happen if you used a bigger or smaller bag? 
  • Could you still create a water cycle in a bag if you laid the bag flat on a table but still in the sun’s rays?

 

  • Photo of the supplies needed to create a water cycle in a bag.
  • Photo of someone using a Sharpie to draw the water cycle on a clear sandwich bag.
  • Photo of the sandwich bag with water cycle drawn on it taped to a window. There is water with blue food color in it.
  • Photo of the bag taped to the window. Water droplets are gathered on the sides of the bag.
  • Photo of the bag taped to the window. Water droplets are falling down the sides of the bag.
  • A lamp is pointed at the bag of water that is taped to the window.