1. Engage students in thinking about how water moves through sediments.

Tell students that much of their water comes from groundwater and that water moves from the ground to the surface. Ask:

• Why does water move through gravel more quickly than it moves through clay? (Gravel is more permeable than clay.)
• Would it be easier to get water out of sand or out of gravel? (It would be easier to get water out of gravel because the pore spaces are larger. The water will move more quickly through larger pore spaces.)

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 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. Introduce and discuss the use of computational models.

Introduce the concept of computational models, and give students an example of a computational model that they may have seen, such as forecasting the weather. The weather forecast provides a good example of how model input is used to predict future conditions. Go to NOAA Weather Forecast Model. Tell students that scientists used current information about the energy and moisture in the atmosphere as an input to the model and that what they see on the weather map is the output of the model's calculations.

5. Have students launch the Groundwater and Surface Water interactive.

Provide students with the link to the Groundwater and Surface Water interactive. Divide students into groups of two or three, with two being the ideal grouping for sharing computer workstations. Inform students they will be working through a series of pages of models with questions related to the models. 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.

Let students know that this is Activity 5 of the Will There Be Enough Fresh Water? lesson.

6. Discuss the issues.

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

• How does the water table affect the relative amount of water in surface bodies and underground? (When the water table is high, meaning the soil is saturated, water will move [or stay] above ground and surface bodies of water will expand. When the water table is low, water will move from the surface down toward the ground.)
• What are the effects on a stream of removing too much water from the ground? (If too much water is removed from the ground, the stream can dry up. The water table can be lowered below the level of the stream.)
• How can humans better manage their use of limited water supplies? (Humans can conserve water. They can use the wastewater to recharge the water supplies.)
• Are rivers an endless supply of fresh water? (Rivers are not an endless supply of fresh water. They can be run dry if the water table goes too low. This can happen when people withdraw too much water from the river and/or from the groundwater that supplies the river. Even though the rivers still receive precipitation, they can be depleted if the water table isn't high enough.)