Math problem set Grade 7 Engineering & Design

Sunhollow Farm Drip Irrigation: Proportional Water Savings

Students compare a fictional farm's sprinkler and drip systems, using proportional reasoning and percent to size the daily and seasonal water they save.

Grade: Grade 7
Subject: Engineering & Design
Material: Math problem set
Time: 40 min
Prep: No prep
Materials: Calculator

Standards

7.RP.A.2 Common Core Math

Recognize and represent proportional relationships between quantities, including identifying the constant of proportionality and representing proportional relationships by equations.

How this material aligns: Problems 1, 2, and 6 treat water use as proportional to run time at a constant flow rate, the direct proportional relationship this standard asks students to recognize and use.

All materials for 7.RP.A.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: Problem 4 finds the percent reduction in water use between the sprinkler and drip designs, the multistep percent-decrease reasoning this standard covers.

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 2026-07-23.

Objectives

Students will use flow rate and run time to calculate the daily water a sprinkler and a drip system each use.
Students will find the percent reduction and the seasonal water saved by switching a farm to drip irrigation.

Vocabulary

Drip irrigation: Watering plants through tubes that release water slowly, drop by drop, right at the roots. Very little water is wasted along the way.
Flow rate: Flow rate measures how much water moves past a point in a certain amount of time, like gallons per minute through a garden hose. Bigger pipes and stronger pushes give bigger flow rates.

Also: proportional, constraint

Teacher overview

Sunhollow Farm is a fictional farm that waters its crops with overhead sprinklers. Sprinklers spray water into the air, and a lot of it drifts or evaporates before it reaches the roots. The farm is thinking about switching to drip irrigation, which drips water slowly right at the base of each plant. This set has students design the switch: they compare how much water each system uses, find the savings, and check the new system against a drought limit.

A common misconception in this math is thinking a lower flow rate always means the plants get too little water. Drip systems use less water because they lose less to the air, not because they starve the plants. Watch for students who assume "less water used" must mean "less water delivered to the roots."

Sunhollow Farm Drip Irrigation: Proportional Water Savings — Grade 7 Engineering & Design

Name: ____________________________ Date: ______________

Problems

Use these values for the fictional Sunhollow Farm design. Each irrigation zone runs once per day.

A sprinkler zone runs at 30 gpm (gallons per minute) for 90 minutes.
A drip zone runs at 12 gpm for 90 minutes.
The farm has 8 zones.

How many gallons does one sprinkler zone use in a day? Multiply the flow rate by the run time.
How many gallons does one drip zone use in a day?
How many gallons of water does the farm save each day for each zone it switches from sprinkler to drip? Use your answers to problems 1 and 2.
What is the percent reduction in daily water use for one zone when the farm switches from sprinkler to drip? Round to the nearest whole percent.
The farm has 8 zones. If every zone switches to drip, how many gallons does the whole farm save in one day? Use your answer to problem 3.
Drip water use is proportional to run time. If one drip zone ran for 120 minutes instead of 90, how many gallons would it use? Use the drip flow rate of 12 gpm.
Over a 60-day growing season, how many total gallons does the switch to drip save across all 8 zones? Use your answer to problem 5.
During a drought, the water district limits the farm to 10,000 gallons per day. The 8 sprinkler zones would use 21,600 gallons per day, which is over the limit. The 8 drip zones use only 8,640 gallons per day. By how many gallons per day does the drip system stay under the 10,000-gallon limit?
In one or two sentences, explain why saving water on a farm matters, using the idea that farming uses a large share of the fresh water people withdraw.

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: 2,700 gallons.
30 gpm × 90 minutes = 2,700 gallons per sprinkler zone per day.
Answer: 1,080 gallons.
12 gpm × 90 minutes = 1,080 gallons per drip zone per day.
Answer: 1,620 gallons.
2,700 − 1,080 = 1,620 gallons saved per zone per day.
Answer: 60%.
1,620 ÷ 2,700 = 0.60, which is a 60 percent reduction.
Answer: 12,960 gallons.
1,620 gallons saved per zone × 8 zones = 12,960 gallons saved per day.
Answer: 1,440 gallons.
Water use is proportional to run time. 12 gpm × 120 minutes = 1,440 gallons.
Answer: 777,600 gallons.
12,960 gallons saved per day × 60 days = 777,600 gallons over the season.
Answer: 1,360 gallons.
10,000 − 8,640 = 1,360 gallons per day under the drought limit.
Answer: Farms use a large share of fresh water, so saving it helps.
Accept any answer noting that agriculture accounts for a large portion of the fresh water people use, so a design that delivers the same crop with less water leaves more for towns, rivers, and future dry years.

Differentiation

Support

Provide a filled-in first row showing "30 gpm × 90 minutes = 2,700 gallons" as a worked model, and give students a printed strip listing the flow rates and run times so they do not have to hunt for them. Allow a calculator throughout.

Extension

Ask students to find the percent reduction in water use for the whole 8-zone farm (not just one zone) and to confirm that it matches the single-zone percent from problem 4. Have them explain why the two percentages are the same.

ELL supports

Pre-teach "sprinkler," "drip," and "flow rate" with a simple side-by-side sketch: water spraying into the air versus water dripping at a plant's base. Provide a sentence frame for problem 9: "Farming uses a lot of fresh water, so saving water on a farm ___."