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Lesson plan Grade 10 Science

Sterling Junction's Aging Water Mains: Evaluating a Fix

A 50-minute grade 10 lesson where students use break rates and costs to evaluate a fictional town's water main replacement plan against reliability trade-offs.

Objectives

  1. Students will calculate the cost and timeline of a water main replacement plan.
  2. Students will evaluate a replacement plan against cost, reliability, and affordability trade-offs.
  3. Students will interpret break-rate and infrastructure-grade data as evidence for a decision.

Vocabulary

Water main
A big underground pipe that carries drinking water beneath the streets to a neighborhood. Smaller service lines branch off it to reach each building.

Also: aging infrastructure, break rate, capital cost, trade-off

Teacher overview

Much of the pipe that carries drinking water in the United States was buried generations ago, and it is wearing out; EPA estimates about $625 billion in drinking-water investment is needed over 20 years, most of it for distribution pipe. This lesson uses the fictional town of Sterling Junction to turn that abstract problem into numbers students can weigh: the cost, the timeline, and the rate increase a replacement plan would require. A common misconception is that a utility can simply replace everything at once; the procedure counters this by having students confront the annual budget limit that forces choices.

Procedure

Hook (5 min): Tell students that a water main breaks somewhere in the United States about every 2 minutes. Ask what a town should do about pipes that are a century old but still working most days. Record a few opinions without judging them.

Direct instruction (12 min): Explain that engineers grade the condition of infrastructure; the 2025 ASCE report card gave US drinking water a C- and wastewater a D+. Introduce the day's decision: the fictional town of Sterling Junction must plan how fast to replace its oldest mains. Suppose replacement costs about $1.5 million per mile in this scenario. Model one calculation on the board: replacing 4 miles at $1.5 million per mile costs 4 x 1.5 = $6 million. Show the units.

Guided practice (10 min): Distribute the handout. Work problems 1 and 2 together: find what percent of Sterling Junction's 60 miles of main is over 100 years old, and the total cost to replace those old miles. Have students confirm each step with a partner.

Independent practice (15 min): Students complete handout problems 3 through 6, finding the replacement timeline, the local break rate per mile, the faster-schedule cost, and a written evaluation of the rate-increase trade-off. Circulate to check that students divide miles by the annual pace correctly.

Formative check (4 min): Ask each student to answer on a card: "At $1.5 million per mile in this scenario, how much does it cost to replace 3 miles?" Scan for the correct product (3 x 1.5 = $4.5 million) before continuing.

Closure (4 min): Have two students state the central trade-off in one sentence each: replacing pipe faster improves reliability but raises rates, while going slower keeps bills lower but risks more breaks. Connect this back to the opening opinions.

Sterling Junction's Aging Water Mains: Evaluating a Fix — Grade 10 Science
Name: ____________________________ Date: ______________

Student Handout

Suppose the fictional town of Sterling Junction has 60 miles of water main, of which 18 miles are over 100 years old. In this scenario, replacement costs about $1.5 million per mile, and the current budget funds 2 miles of replacement per year. Last year the town recorded 24 main breaks.

  1. What percent of Sterling Junction's 60 miles of main is over 100 years old? Use the 18 old miles.
  2. At $1.5 million per mile, what is the total cost to replace all 18 of the old miles?
  3. At the current pace of 2 miles per year, how many years will it take to replace all 18 old miles?
  4. The town recorded 24 main breaks last year across its 60 miles. What was the break rate in breaks per mile?
  5. To finish the 18 old miles in 6 years instead, how many miles per year must the town replace, and what would that faster pace cost each year at $1.5 million per mile?
  6. National water and sewer bills rose about 24 percent from 2019 to 2024. In two or three sentences, evaluate the trade-off Sterling Junction faces if it raises rates to fund the faster 6-year plan, naming one benefit and one drawback.

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

Answer Key
  1. Answer: 30 percent. 18 old miles divided by 60 total miles = 0.30, or 30 percent of the system.
  2. Answer: $27 million. 18 miles x $1.5 million per mile = $27 million total.
  3. Answer: 9 years. 18 miles divided by 2 miles per year = 9 years at the current pace.
  4. Answer: 0.4 breaks per mile. 24 breaks divided by 60 miles = 0.4 breaks per mile last year.
  5. Answer: 3 miles per year, at $4.5 million per year. 18 miles divided by 6 years = 3 miles per year, and 3 x $1.5 million = $4.5 million each year.
  6. Answer: Accept any answer that names a real benefit and a real drawback. A benefit of raising rates is faster replacement, which means fewer breaks and more reliable service; a drawback is that higher bills strain households, and rates have already risen about 24 percent nationally from 2019 to 2024, so affordability is a real concern.

Differentiation

Support

Provide the cost example (4 miles at $1.5 million per mile) worked out at the top of the handout, and give students the division set up for problems 1 and 3 so they can focus on interpreting the results.

Extension

Have students design a two-tier plan that replaces the 5 worst miles in the first year, then slows to a sustainable pace, and calculate both the first-year cost and the total timeline, then argue whether the faster start is worth the higher first-year rate.

ELL supports

Pre-teach "water main," "break rate," "capital cost," and "trade-off" with a labeled picture of a buried pipe and a street repair. Provide sentence frames for problem 6, such as "Raising rates would help because ___, but it would hurt because ___."