1. Engage students in thinking about how fresh water is used.

Tell students in this activity they will be taking a close look at how humans use water—both in direct and indirect ways. They will examine the relationship between freshwater distribution and populations, and they will analyze the costs and benefits of putting dams on rivers and streams. To begin, ask: How do you use fresh water? (Student answer will vary, but will include examples like the following: Fresh water is used for drinking, bathing, flushing toilets, and irritating. Freshwater is also used in electricity production and manufacturing.)

2. Discuss the role of uncertainty in the scientific process.

Tell students that science is a process of learning how the world works and that scientists do not know the “right” answers when they start to investigate a question. We can see examples of scientists' uncertainty in the forecasting of precipitation amounts. Have students go to the NOAA National Weather Service. Ask them to input their zip codes, hit “Go”, scroll down to the bottom of the page, and click on the “Hourly Weather Graph”. This page shows the hourly weather forecast for your area. The first box shows the predicted temperature and dew point (along with wind chill or heat index, when applicable). The second box shows the predicted wind speed and direction. The third box shows the predicted sky cover (i.e. cloud cover), relative humidity, and chance for precipitation. The boxes below that line show whether the precipitation is likely to be rain, snow, freezing rain, or sleet. Point out the line for precipitation potential (the brown line). Ask:

• Why is the precipitation shown as a “%”? (Precipitation is dependent on other factors, such as relative humidity and temperature. It is more likely to precipitate when the temperature is the same as or lower than the dew point.) 
• If there is a likelihood of precipitation, why is the amount of rain/snow shown as ranges? (The amount of precipitation that will fall is dependent on the amount of moisture in the atmosphere. The atmosphere is continually changing, so the amounts are guidelines for what could happen rather than perfect predictions.) 

  *If there is no or low likelihood of precipitation in your area, you may want to find a different location (in the United States) that has a higher likelihood of precipitation. You can look at a current weather map (radar) to find where in the United States precipitation is happening currently. Your students will then be able to see scientists' forecasts of precipitation amounts represented as a range overlaid on the bar graphs.

   

Tell students they will be asked questions about the certainty of their predictions and that they should think about what scientific data are available as they assess their certainty with their answers. Encourage students to discuss the scientific evidence with each other to better assess their level of certainty with their predictions.

3. Introduce the concept of systems in Earth's water resources.

Tell students that forecasting what will happen to Earth's fresh water supplies is a complicated process because there are many different interacting parts. Tell students that scientists think about how one part of the system can affect other parts of the system. Give students a simple example of a system, as described in the scenario below.

On an island, there is a population of foxes and a population of rabbits. The foxes prey on the rabbits. Ask: 

• When there are a lot of rabbits, what will happen to the fox population? (It will increase because there is an ample food supply.) 
• What happens to the fox population when they’ve eaten most of the rabbits? (The foxes will die of starvation as their food supply decreases.) 
• What happens to the amount of grass when the fox population is high? (The amount of grass will increase because there are fewer rabbits to eat the grass.)
• If there is a drought and the grass doesn’t grow well, what will happen to the populations of foxes and rabbits? (The rabbit population will decrease because they have a lesser food supply. The fox population should also decrease as their food supply decreases.)

Humans introduce dogs to the island. The dogs compete with the foxes over the rabbit food supply. Ask: What will happen to the populations of foxes, rabbits, and grass after the dogs are introduced? (The foxes will decrease because they are sharing their food supply, the rabbits will decrease because they have more predators, and the grass will do well because of the lowered impact of the smaller rabbit population.)

Tell students that simple cause-effect relationships can expand into more complex system relationships. Let students know that they will be exploring the relationship between how sediments and rock types affect groundwater movement. Encourage students to think about how human actions play a role in changes in the flow of water and in freshwater availability.

4. Have students launch the Using Fresh Water interactive.

Provide students with the link to the Using Fresh Water interactive. Divide students into groups of two or three, with two being the ideal grouping to allow groups to share a computer workstation. Tell students that they will be working through a series of pages of data with questions related to the data. Ask students to work through the activity in their groups, discussing and responding to questions as they go.

NOTE: You can access the Answer Key for students' questions—and save students' data for online grading—through a free registration on the High-Adventure Science portal page.

Tell students that this is Activity 3 of the Will There Be Enough Fresh Water? lesson.

5. Discuss the issues.

After students have completed the activity, bring the groups back together and lead a discussion focusing on these questions:

• Even if you live in an area where fresh water is plentiful, why do you have to be concerned about the freshwater supply? (You should still be concerned about the freshwater supply because it can be contaminated by human actions. This would make the fresh water useless even if there was a lot of it.) 

• Are the benefits of dams worth the costs of dams? (Answers will vary. Some of the benefits of dams are flood control, recreation, and electricity production. Some of the costs of dams are habitat disruption, sediment depletion of river deltas, and loss of surrounding land.) 

• What are some ways that humans have affected the quantity and quality of water supplies around the world? (Humans have changed the surface, which has allowed less water to infiltrate the surface. They have pulled water out of very deep aquifers in desert areas. They have inadvertently contaminated some water supplies.)