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Watersheds and Water Flow

In this demonstration, students will learn what watersheds are and how they impact our local waters.

To understand the importance of water and water conservation, we must first understand how water interacts with the world around us. This activity demonstrates how water moves, and how water collects.

Most of the Earth’s water is found in the ocean. Water evaporates from the ocean, lakes and rivers and condenses into clouds. When these clouds fill with water, the water will eventually fall as precipitation. Precipitation can be rain, snow, hail or sleet. Once the rain hits the ground it will flow downward following the path of least resistance. For some of the water, this is in the form of infiltration, which means that the water flows through the soil to the ground water. For some water this is in the form of surface flow or runoff in creeks and rivers. In both cases, the water will continue to flow and pick up minerals, nutrients and pollution, until it reaches a body of water that is at low elevation. For most water, this ends up being the ocean. Then, evaporation continues the cycle.

Direction of water flow can be predicted based on the ground’s elevation and soil type. An area where all water drains to the same river or body of water is called a watershed. A simple way to imagine this is using a shower analogy. When water moves from the shower heads (and ‘rains’), the water will hit the shower curtains, the walls and the bottom of the shower. All the areas that the shower head water hits is part of the same ‘watershed’, because it will all flow down into the same ‘river’, the drain pipe.

In Metro Vancouver, there are three separate watersheds that we use to collect water into a storage body or reservoir. Over half of BC’s population uses these three reservoirs as our source of drinking water.

In our modern age, we transport water from one watershed to another in many ways.

  • We transport bottled water collecting it from one place and sending it to another.
  • We transport food, which is full of water, from country to country.
  • We pipe water away from a watershed to be used in irrigation for our agriculture.

If we take water out of one watershed faster than it is replenished (by precipitation, or mountain glaciers melting) then our reservoirs will slowly decrease in size.


  • Describe a watershed and how water flows through the environment.

  • Describe methods and the importance of water conservation.

  • Explore the effects of water pollution.


  • Per Class or Group:
    2 turkey basters or eye droppers
    2 cups of water
    2 deep clear baking trays
    2 pieces of brown paper
    1 bottle of food colouring
    4 thick books (at least 2 to help prop up each tray)
    1 black marker
    plasticine for creating landscapes

Key Questions

  • What is a watershed?
  • How does water flow through its environment?
  • Where does our pollution end up? What about our litter, like plastic bags?
  • What are some ways that we may be displacing water and affecting our reservoir water levels?
  • Although we can reduce the amount of water in a given area, will the water cycle stop all together?

What To Do


  1. Prop up both baking trays at an angle (~ 45°) using books to create one high elevation edge and one low elevation edge. Each baking tray represents a watershed.
  2. Tape a piece of paper to the inside of each baking tray. Label these papers SOIL using the black marker.
  3. Add some plasticine to create mountains or landscape
  4. Put a few drops of food colouring on each piece of paper and around the plasticine. These drops represent minerals, nutrients, or pollution.
  5. Pour 1 cup of water on the low edge of each baking dish. This represents a reservoir, ocean, lake, or any body of water.
  6. Pick two volunteers, one for each watershed.
  7. Hand out a turkey baster or eye dropper to each volunteer.


  1. Using the turkey baster or eye dropper, have the volunteers suck up water from the reservoir at the lowest point of the watershed. This water is evaporating.
  2. Then, have the volunteers release the water at the top most spot of the baking tray. This water is raining back down.
  3. Observe how the water flows downwards. Note that some water is infiltrated into the soil, and some flows on top flowing back down to the same body of water.
  4. Have the volunteers repeat steps 1-3 a few times. Notice that as the water flows on the surface and in the soil, it picks up some of the minerals, nutrients, and pollution found in the soil. These minerals, nutrients and pollution all flow into the same body of water as well.
  5. Then, have the volunteers suck up water from one body of water using both turkey basters.
  6. This time, release the water into the other watershed.
  7. Note that even though there is the same amount of water in total, by displacing the water, one reservoir will decline in size.


  • Get a map of your region. Follow the flow of water through your closest watersheds. Where does the water start? Where does it end?
  • Where does your drinking water come from?
  • Where does your wastewater go?

Other Resources

MetroVancouver | Watersheds & Reservoirs