Project Grade 9 Engineering & Design

Cotton Bend Brackish Well: A Reverse-Osmosis Pilot Design Project

A grade 9 engineering project where teams design a reverse-osmosis pilot system for a brackish well, budgeting cost, capacity, and energy for a fictional water district.

Grade: Grade 9
Subject: Engineering & Design
Material: Project
Time: 4 sessions, ~200 min total
Prep: Moderate prep
Materials: Grid paper for system diagrams, Rulers, Calculators, Teacher-provided component price sheet, Brackish-water and reverse-osmosis reference sheet

Standards

HS-ETS1-2 NGSS

Design a solution to a complex real-world problem by breaking it down into smaller, more manageable problems that can be solved through engineering.

How this material aligns: Milestone 1 breaks the overall design problem into smaller solvable pieces, an energy-cost calculation, a capacity target, and a space constraint, exactly the decomposition this standard requires.

All materials for HS-ETS1-2 →

HS-ETS1-3 NGSS

Evaluate a solution to a complex real-world problem based on prioritized criteria and trade-offs that account for a range of constraints, including cost, safety, reliability, and aesthetics as well as possible social, cultural, and environmental impacts.

How this material aligns: Milestone 3 requires teams to evaluate their two competing draft layouts from Milestone 2 against prioritized constraints, cost, capacity, and energy use, before selecting and refining one final design, exactly the trade-off evaluation this standard describes.

All materials for HS-ETS1-3 →

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This material is in the public domain (CC0) and may be copied, edited, and shared freely, without attribution. Updated 2026-07-15.

Objectives

Students will calculate the estimated daily energy cost of a reverse-osmosis pilot system using a stated energy-use range and electricity rate.
Students will design a treatment system layout that meets a stated capacity target within a fixed budget and space constraint.
Students will evaluate two competing design drafts using cost-benefit reasoning and select one to refine.

Vocabulary

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.
Brackish water: Water that is saltier than fresh water but not as salty as the ocean. It is found where rivers meet the sea and in some groundwater.
Total dissolved solids (TDS): Total dissolved solids is a measure of everything dissolved in water that you cannot see or filter out, like minerals and salts. Water with very high TDS can taste salty or bitter, even though it might look perfectly clear.
Membrane filtration: Membrane filtration pushes water through a very thin material full of microscopic holes that let water molecules pass but block out particles, bacteria, and sometimes even viruses. Many modern treatment plants use it as a newer alternative to traditional sand filters.

Teacher overview

Cotton Bend (a fictional inland town invented for this project) recently drilled a new municipal well to serve a growing subdivision, but the well struck a naturally salty layer of the aquifer, leaving the water brackish, saltier than fresh water but not as salty as seawater, and unpleasant to drink. Over four sessions, student engineering teams design a small-scale reverse-osmosis pilot system, a membrane-based treatment method that forces water through a very fine filter to remove dissolved salts, to treat a portion of the well's output before the town commits to a full-scale system. Teams work within a fixed budget, a capacity target, and an energy-cost estimate, then present their design to a fictional review board.

Cotton Bend Brackish Well: A Reverse-Osmosis Pilot Design Project — Grade 9 Engineering & Design

Name: ____________________________ Date: ______________

Project Brief

Driving question: How can we design a reverse-osmosis pilot system that treats at least 5,000 gallons per day of Cotton Bend's brackish well water within a $15,000 budget and a reasonable energy cost?

Scenario: The Cotton Bend Water District Board is a fictional board invented for this project. The board has asked student engineering teams to propose a pilot reverse-osmosis system. It wants to see what a pilot would cost before it decides whether to pay for full-scale treatment at the new well.

Constraints:

Budget: $15,000 total for the membrane unit, pre-filters, pump, and piping. This is a fictional budget for the project. Your teacher provides a component price sheet.
Capacity: the pilot system must be sized to treat at least 5,000 gallons per day.
Energy: treating seawater by reverse osmosis takes roughly 11 to 15 kilowatt-hours (kWh) per 1,000 gallons. Brackish groundwater like Cotton Bend's usually takes less energy, because it holds less dissolved salt. This project does not give a brackish-specific figure, so this project uses the seawater figure as a conservative, high-side planning estimate. Assume Cotton Bend's utility pays $0.12 per kilowatt-hour, a planning rate set for this project.
Space: the pilot system must fit within a 10-foot by 10-foot equipment pad.

Final deliverable: A labeled system diagram, drawn to scale, showing the pre-filter, membrane unit, pump, and storage. Teams also write a one-page proposal to the Cotton Bend Water District Board. The proposal explains how the design meets the budget, capacity, and energy constraints.

Milestones

Session 1 -- Research and calculate the energy baseline: Teams learn what makes water brackish and why reverse osmosis removes dissolved salts. Then they estimate the daily energy cost of treating 5,000 gallons, using the energy range and electricity rate above. Working example: 5,000 gallons divided into 1,000-gallon units gives 5 units. At 11 to 15 kWh per unit, that is 55 to 75 kWh per day. At $0.12 per kWh, that is $6.60 to $9.00 per day. Output: a completed energy-cost worksheet showing both the low-end and high-end estimates.
Session 2 -- Draft two design layouts: Teams sketch two different pilot layouts on grid paper. Each layout arranges the pre-filter, membrane unit, and pump a different way, and each must fit the 10-by-10-foot pad. Teams estimate a rough cost for each layout using the teacher's price sheet. Output: two labeled draft diagrams with rough cost estimates.
Session 3 -- Choose and refine one design: Teams compare their two drafts against the budget, capacity, and energy constraints. They use cost-benefit reasoning to weigh the tradeoffs each design makes. Then they choose one design and refine it into a final scaled system diagram. The itemized costs must total $15,000 or less. Output: one final system diagram with an itemized cost list.
Session 4 -- Write and present the proposal: Teams write the one-page proposal explaining their design choices. Then they present the diagram and proposal to the class in a role-play of a Cotton Bend Water District Board meeting. Output: a completed written proposal and a short team presentation.

From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.

Rubric

Criterion	Emerging	Developing	Proficient	Advanced
Capacity target	Design does not address the 5,000-gallon-per-day target	Design references the target but the diagram does not clearly show how it is met	Diagram and proposal clearly show how the design treats at least 5,000 gallons per day	Diagram and proposal show the target met with a clear margin and explain the reasoning
Budget constraint	Total cost exceeds $15,000 with no adjustment	Total cost is close to $15,000 but not verified with itemized costs	Total cost is at or under $15,000 with an itemized cost list	Total cost is at or under $15,000, itemized, with a brief explanation of a tradeoff the team made to stay within budget
Energy-cost reasoning	Energy cost is not calculated or is calculated incorrectly	Energy cost is calculated but the low-end and high-end estimates are not distinguished	Energy cost is calculated correctly, showing both the low-end and high-end daily estimates	Energy cost is calculated correctly and the proposal explains why brackish water likely costs less to treat than the seawater figure used
Presentation and proposal	Proposal is incomplete or difficult to follow	Proposal covers the design but lacks clear reasoning	Proposal clearly explains how the design meets all three constraints	Proposal clearly explains all three constraints and anticipates a likely question from the review board

Differentiation

Support (below grade level)

Provide the energy-cost calculation from Milestone 1 already worked out, so teams can focus their time on the design and budget work in Sessions 2 through 4. Provide a simplified price sheet with fewer component choices.

Extension (above grade level)

Ask teams to calculate how much the daily energy cost would change if Cotton Bend's brackish water actually required only half the seawater energy figure, and to explain in their proposal why using the more conservative, higher figure was still a reasonable planning choice.

ELL supports

Provide a labeled diagram of a reverse-osmosis system's cross-section (pre-filter, membrane, concentrate outlet, treated-water outlet) before Session 1. Allow the written proposal to include labeled sketches alongside shorter sentences rather than full paragraphs.