Writing prompt Grade 6 Social Studies & Civics
Should Dune Harbor Build a Desalination Plant? A Grade 6 Argument
A grade 6 argument writing prompt where students take a position on whether a fictional drought-stricken coastal town should build a reverse-osmosis desalination plant.
Objectives
- Students will write an argument that states a claim and supports it with reasons and evidence.
- Students will use real capacity and energy figures from an existing desalination plant to evaluate a water-supply decision.
Vocabulary
- Desalination
- Turning salty water, like ocean water, into fresh water people can use. It works, but it takes a lot of energy and leaves behind very salty water that must be handled carefully.
- Reverse osmosis
- Reverse osmosis cleans water by pushing it through a membrane with holes so tiny that salt and most other dissolved things cannot fit through. It can even turn seawater into fresh water.
Also: claim, evidence
Teacher overview
Dune Harbor, a fictional coastal town used for this prompt, is in its third year of drought and is deciding whether to build a reverse-osmosis desalination plant to secure its water supply from the ocean. Desalination guarantees a water source that a drought cannot shrink, but it uses far more energy than treating fresh water from a river or reservoir. This prompt asks students to take a position on that tradeoff using real figures from an existing desalination plant as their evidence.
Prompt
Background: Desalination plants remove salt from seawater. Most of them use a process called reverse osmosis. This process pushes seawater through a membrane. The membrane lets water molecules through but blocks the salt.
The Carlsbad, California desalination plant is the largest in the country. It uses reverse osmosis, and it produces about 50 million gallons of drinking water per day. That is roughly 10 percent of San Diego County's total water supply.
Reverse osmosis uses a lot of energy. It takes about 11 to 15 kilowatt-hours for every 1,000 gallons treated. Regular treatment of river or reservoir water takes only about 1 to 2 kilowatt-hours for the same amount. A desalination plant also costs more to build than a regular plant. But it draws water from the ocean. The ocean does not run dry during a drought. A river or reservoir can run dry.
Writing task: Dune Harbor's town council must decide whether to fund a desalination plant like Carlsbad's. Write an argument. State a clear claim on whether Dune Harbor should build the plant. Give at least two reasons for your position. Support each reason with evidence from the background material above.
Planning Organizer
| Category | Your notes |
|---|---|
| Claim (should Dune Harbor build the plant?) | |
| Reason 1 + evidence from background material | |
| Reason 2 + evidence from background material | |
| Concluding statement |
From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.
Exemplar & Rubric
Exemplar response:
Dune Harbor should build a desalination plant, because a water source that a drought cannot shrink is worth its higher cost and energy use. The Carlsbad desalination plant in California shows this approach can work at a real scale: it produces about 50 million gallons of drinking water every day, supplying roughly 10 percent of San Diego County's needs. A town like Dune Harbor, three years into a drought, cannot count on a river or reservoir that keeps getting lower every summer.
A second reason Dune Harbor should build the plant is that the ocean is a source the town can always count on, even in a dry year. Reverse osmosis does use more energy than treating water from a river, about 11 to 15 kilowatt-hours per 1,000 gallons compared to about 1 to 2 kilowatt-hours for conventional treatment. That extra energy costs money, but it buys something a conventional plant cannot: water that keeps flowing no matter how little rain falls.
Dune Harbor's town council should approve the desalination plant. The Carlsbad example proves the technology works at a meaningful scale, and the extra energy cost is a reasonable price for a water supply the drought cannot take away.
Rubric:
| Criterion | Emerging | Developing | Proficient | Advanced |
|---|---|---|---|---|
| Claim | No clear position stated | States a position but it shifts or is unclear | States one clear, consistent position on funding the plant | States a clear position and previews the reasons that will follow |
| Evidence & reasoning | No evidence from the background material | Restates one fact without explaining how it supports the claim | Uses at least one specific figure from the background material and explains how it supports the claim | Uses two or more specific figures and explains how each one supports the claim |
| Organization & conventions | Ideas are disconnected; frequent errors interfere with meaning | Some organization present; errors are noticeable but do not block meaning | Clear paragraph structure with a claim, reasons, and a conclusion; few errors | Clear, purposeful structure with a strong concluding statement; virtually error-free |
Differentiation
Support (below grade level)
Provide sentence starters for each Planning Organizer row ("Dune Harbor should/should not build the plant because ___, and the background material shows ___.") and allow students to write only two shorter paragraphs, one for each reason, instead of a full three-paragraph response.
Extension (above grade level)
Ask students to work out, using only the background material provided, what percent of San Diego County's water supply Carlsbad does not provide, and add a sentence to their conclusion addressing what Dune Harbor would still need besides a desalination plant.
ELL supports
Pre-teach "desalination," "claim," and "evidence" with visuals (an ocean-to-tap diagram for desalination, a highlighter icon for evidence) before the writing task begins. Allow the Planning Organizer to be completed with short phrases rather than full sentences before drafting starts.