Lesson plan Grade 7 Engineering & Design

Mossgrave Courts Greywater: Choosing an Irrigation Layout

A 50-minute grade 7 lesson matching laundry greywater supply to courtyard irrigation demand, then screening three layouts against a coverage target and a budget.

Grade: Grade 7
Subject: Engineering & Design
Material: Lesson plan
Time: 50 min
Prep: Low prep
Materials: Printed copies of the student handout, Calculators

Standards

MS-ETS1-1 NGSS

Define the criteria and constraints of a design problem with sufficient precision to ensure a successful solution, taking into account relevant scientific principles and potential impacts on people and the natural environment that may limit possible solutions.

How this material aligns: Students convert the owner's request into a numbered coverage target, a surge storage requirement, and a budget ceiling before any layout is chosen.

All materials for MS-ETS1-1 →

MS-ETS1-2 NGSS

Evaluate competing design solutions using a systematic process to determine how well they meet the criteria and constraints of the problem.

How this material aligns: Handout questions 6 through 10 screen three competing layouts against the coverage criterion and the budget limit, a systematic comparison rather than a preference.

All materials for MS-ETS1-2 →

7.RP.A.3 Common Core Math

Use proportional relationships to solve multistep ratio and percent problems. Examples: simple interest, tax, markups and markdowns, gratuities and commissions, fees, percent increase and decrease, percent error.

How this material aligns: Handout questions 3 and 5 ask what percent of weekly demand each layout supplies, multistep percent comparisons built from volumes students computed.

All materials for 7.RP.A.3 →

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This material is in the public domain (CC0) and may be copied, edited, and shared freely, without attribution. Updated 2026-09-23.

Objectives

Students will compute a weekly greywater supply from fixture counts and a per-load volume.
Students will express each layout's supply as a percent of weekly irrigation demand.
Students will size a surge tank from a peak-day volume and a list of stock sizes.

Vocabulary

Greywater: Gently used water from showers, bathtubs, bathroom sinks, and washing machines. With the right setup, it can be reused to water plants instead of going down the drain.
Surge tank: A surge tank is a tank connected to a pipeline that gives water somewhere to go when a pump suddenly stops or a valve slams shut, absorbing the shock instead of letting it slam through the pipes. It helps prevent the loud banging and pipe damage known as water hammer.

Also: subsurface drip, demand, criterion, peak day

Teacher overview

The owner of a fictional apartment building called Mossgrave Courts wants laundry water to irrigate the courtyard instead of running to the sewer. Three layouts are on the table, and students decide among them by matching supply to demand, sizing a surge tank, and checking costs. The misconception worth addressing head on is that a system supplying more water is automatically the better design. Students who hold it will pick whichever layout collects from the most apartments and stop there, missing that the water arrives in bursts on laundry day while the plants need it spread across the week. That is why the surge tank question exists, and it is worth saying so before students reach question 7.

Procedure

Hook (5 min): Describe the fictional courtyard, currently watered from a hose bib, and the laundry room running its water to the sewer. Ask students what they would need to know before saying whether the swap would work. Write their questions on the board and mark the two that amount to supply and demand.

Direct instruction (10 min): Define greywater as used water from laundry, showers, and bathroom sinks, with no toilet water. Introduce the two conversions of the day. Weekly laundry greywater equals units times loads per unit per week times gallons per load. Irrigation demand in gallons equals the planted area in square feet times the watering depth in inches times 0.623. Model both on a site students will not be asked to key. A fictional duplex with 2 units, each running 4 loads a week at 25 gallons, produces 200 gallons a week, while a 500-square-foot bed watered half an inch deep needs 500 times 0.5 times 0.623, or about 156 gallons. Name the design problem: the owner will fund a layout only if it supplies at least 75 percent of the courtyard's weekly demand.

Guided practice (12 min): Distribute the handout. Work questions 1 through 3 together so every student has the building's weekly supply, the courtyard's weekly demand, and the percent of demand met. Pause after question 3 and ask whether meeting 96 percent of the weekly total guarantees that the plants are watered properly. Collect two or three answers without resolving them.

Independent practice (18 min): Students complete questions 4 through 11 in pairs. Circulate and check that pairs are dividing supply by demand rather than the reverse in question 5. Pairs who finish early should write a sentence explaining why the tank in question 8 is sized from one day rather than from the week.

Closure and formative check (5 min): Collect the handouts and scan question 6 only. If more than a quarter of the class answers yes, reteach the coverage criterion at the start of the next session by putting the 32 percent figure next to the 75 percent target on the board. Close by asking one pair to read their question 11 answer.

Mossgrave Courts Greywater: Choosing an Irrigation Layout — Grade 7 Engineering & Design

Name: ____________________________ Date: ______________

Student Handout

Suppose you are designing the greywater system at the fictional Mossgrave Courts. Use these figures for every question.

The building has 24 apartments, 8 of them on the ground floor. Each apartment runs 3 loads of laundry a week. Each load discharges 25 gallons of greywater. The courtyard has 4,000 square feet of planting and needs 0.75 inch of water each week in summer. Irrigation demand in gallons equals area in square feet times depth in inches times 0.623. On the busiest laundry day the building runs 10 loads. The owner will fund a layout only if it supplies at least 75 percent of weekly demand. The budget is 12,000 dollars.

The three layouts are:

Layout	How it works	Apartments served	Cost
A	Pipes run by gravity from ground-floor machines straight to mulch basins	The 8 ground-floor apartments	3,500 dollars
B	All machines drain to one surge tank, which gravity-feeds buried drip lines	All 24 apartments	9,800 dollars
C	All machines drain to a sand filter and a pump that feeds buried drip lines	All 24 apartments	15,200 dollars

Stock surge tanks come in three sizes: 150 gallons, 300 gallons, and 500 gallons.

How many gallons of laundry greywater does the whole building produce in one week?
How many gallons of water does the courtyard need in one week?
What percent of the courtyard's weekly demand could the whole building's greywater supply? Round to the nearest whole percent.
Layout A collects from the 8 ground-floor apartments only. How many gallons a week does Layout A supply?
What percent of the courtyard's weekly demand does Layout A supply? Round to the nearest whole percent.
The owner's criterion is at least 75 percent of weekly demand. Does Layout A meet it?
On the busiest laundry day the building runs 10 loads. How many gallons of greywater arrive that day?
A surge tank must hold the whole busiest day. Which stock tank is the smallest one that works?
Which layouts cost 12,000 dollars or less?
Using your answers to questions 6 and 9, which single layout should you recommend?
Buried drip lines must never let greywater pond on the surface. Name one measurement or check a maintenance worker could make in the courtyard to find out whether that requirement is being met, and say how often it should be done.

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

Answer Key

Answer: 1,800 gallons.
24 apartments times 3 loads times 25 gallons equals 1,800 gallons a week.
Answer: 1,869 gallons.
4,000 square feet times 0.75 inch times 0.623 equals 1,869 gallons a week.
Answer: 96 percent.
1,800 divided by 1,869 equals 0.963, which is 96 percent to the nearest whole percent.
Answer: 600 gallons.
8 apartments times 3 loads times 25 gallons equals 600 gallons a week.
Answer: 32 percent.
600 divided by 1,869 equals 0.321, which is 32 percent to the nearest whole percent.
Answer: No.
Layout A supplies 32 percent of weekly demand, which is below the 75 percent criterion, so it fails.
Answer: 250 gallons.
10 loads times 25 gallons equals 250 gallons on the busiest day.
Answer: The 300-gallon tank.
The tank must hold at least 250 gallons. The 150-gallon tank is too small, and the 300-gallon tank is the smallest stock size that holds the full day.
Answer: Layouts A and B.
Layout A costs 3,500 dollars and Layout B costs 9,800 dollars, both within the 12,000-dollar budget. Layout C costs 15,200 dollars, which is over.
Answer: Layout B.
Layout A fails the coverage criterion at 32 percent. Layout C would meet coverage but costs more than the budget allows. Layout B supplies 96 percent of demand for 9,800 dollars, so it is the only layout that clears both requirements.
Answer: A named check with a stated frequency.
Accept any observation a worker could actually make, paired with a frequency. Common correct answers include walking the drip lines after the heaviest laundry day and looking for wet spots or ponding, checking each mulch basin for standing water within an hour of a tank discharge, watching for odor near the lines, probing the soil with a screwdriver to see whether water sits at the surface, and inspecting emitters monthly for clogs that would push water back to one spot. Weekly during summer and after any tank discharge are both reasonable frequencies. Do not accept an answer that names only a device the building does not have.

Differentiation

Support

Give these students a handout copy with questions 1 and 2 already set up as multiplication strings so their work starts at the arithmetic. Provide a labeled bar showing weekly demand with the 75 percent line marked, so questions 3, 5, and 6 can be checked against a picture. Supply a two-column elimination table for question 10 with the headings written in.

Extension

Have students find the smallest number of apartments that would have to be plumbed into Layout B for it to still clear the 75 percent criterion, and explain what that tells the owner about phasing the work over two summers. Ask them to redo question 2 for a courtyard that needs 1 inch a week and report whether the recommendation changes.

ELL supports

Pre-teach greywater, demand, and surge with a labeled diagram showing a washing machine, a tank, and buried lines under a planting bed. Provide the frames "Supply is ____ gallons and demand is ____ gallons" and "Layout ____ fails because ____." Allow question 11 to be answered with a labeled sketch of the courtyard and two short captions.

Extensions

Ask students to write a short posting for the fictional building's laundry room explaining which detergents the new system requires and why, given that the water now goes to plants rather than to a treatment plant. Have them check their posting against the design decision they made, since a layout that serves all 24 apartments depends on every resident following the same rule.