Desalination
Governor Seeks Solution to Water Shortage
A water shortage in California.
The governor has declared that removing salt from ocean water can help California’s water shortage.
Desalination as a potential solution.
The governor’s advisors point out that 97% of the Earth’s water is in the oceans. However, ocean water is salty and cannot be drunk. If salt can be removed from ocean water with a process called desalination, a lot of previously undrinkable ocean water can be used to help the water shortage.
Two methods of desalination.
The governor has been informed that one method of desalination is to heat ocean water so that it turns into water vapor. This leaves the salt behind. The water vapor is then passed over a cold object, causing it turn back into clean liquid water. This is called the evaporation method.
The governor has also been made aware of another method of desalination that involves pushing ocean water through a membrane, which is a sheet with tiny holes in it. Only the water particles pass through the membrane, leaving all the salt behind. This is called the membrane method.
Which desalination method is better?
The governor has learned that the membrane method produces a messy sludge called brine that can be harmful to ocean animals when dumped back into the ocean. However, the governor is also told that heating water with the evaporation method requires more energy than the membrane method. Increased energy consumption can be expensive for California.
Note: The numerical scores indicated in the scoring rubrics were for research purposes. Higher scores indicate higher quality argumentation. We encourage you to use a scoring scheme that matches your present goals for students.
1 What is the main claim that is being made by the governor?
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| Level | Description | Student Responses |
|---|---|---|
| 2 |
Student report of the main claim includes something referring to a water shortage as a problem that needs to be solved and something about removing salt from ocean water (desalination) as a possible solution. |
The governor has declared that removing salt form ocean water can help California’s water shortage. That he thinks if we remove salt form the ocean, it can help the water shortage. |
| 1 |
Student refers to either something about a water shortage as a problem that needs to be solved or something about removing salt from ocean water (desalination) as a possible solution, but not both. |
Is to remove salt from water by desalination. I think that using Desalination as a potential solution would be good but we are also harming the sea animals. The governor wants to find a solution to the water shortage in California. He’s trying to save the water & he’s trying to change it. Remove salt from ocean to get fresh drinkable water. |
| 0 |
Student refers to neither something about a water shortage as a problem that needs to be solved nor something about removing salt from ocean water (desalination) as a possible solution. |
Which desalination method is better. I think evaporation method is better and the governor wants the opinion. That the water is being wasted! |
2 – 4 For each of these questions, indicate the best answer.
- What might be a reason why the governor thinks desalination can help the water shortage?
- Some recommend to the governor that the evaporation method is better, what would be a reason that they could use in their argument?
- Some recommend to the governor that the membrane method is better, what would be a reason that they could use in their argument?
5 Which desalination method would you recommend to the governor? Compare the two methods and determine which one is better.
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| Level | Description | Student Responses |
|---|---|---|
| 2 |
Student provides a feasible reason for why the evaporation method or the membrane method is better (doesn’t matter which method they chose, as long as they provide a reason for why they made their selection), and the student provides another feasible, but different reason for why the method they didn’t recommend to the governor is worse. (Students mention something about the trade- off between energy consumption and waste.) |
I say the evaporation method is better than the membrane method because the evaporation method is safe but cost a lot of money but it is better than the membrane method that can kill a lot of ocean animals, The evaporation method is way better than the membrane method. Even if we are using a lot of energy to get clean water I wouldn’t choose the membrane one because it can kill sea animals. |
| 1 |
Student provides a feasible reason for why the evaporation method or the membrane method is better (doesn’t matter which method they chose, as long as they provide a reason for why they made their selection), but they do not provide a feasible, but different reason for why the method they didn’t recommend to the governor is worse. (Students focus on energy consumption, or waste, but not both.) |
The evaporation method because it doesn’t harm anyone. The membrane because it doesn’t take up a lot of energy and harmless to ocean life. I think the evaporation method is better because it doesn’t harm other animals. The membrane method because if you still get brine do not dump it into the ocean. The evaporation method because it won’t harm the animals and it will be safe. The evaporation method is better because if water evaporates it will clean the water and leave all the salt and gunk behind. |
| 0 |
Student does not provide a feasible reason for why the evaporation method or the membrane method is better. (Students fail to focus on energy consumption or waste.) |
Reason 3 because he wants to help change it. To save water. 3 because it is more smarter. |
