Lesson plan Grade 12 Social Studies & Civics

Designing Calderwood's Water Rates: A Cost-of-Service Workshop

A capstone grade 12 economics workshop in which students design a water rate structure for a fictional city and analyze how each option shifts costs among households.

Grade: Grade 12
Subject: Social Studies & Civics
Material: Lesson plan
Time: 55 min
Prep: Low prep
Materials: Printed rate-option handout, Calculators, Index cards

Standards

D2.Eco.1.9-12 C3 Framework

Analyze how incentives influence choices that may result in policies with a range of costs and benefits for different groups.

How this material aligns: Students analyze how a fixed charge and an increasing-block rate act as incentives whose costs and benefits fall differently on low, median, and high water users.

All materials for D2.Eco.1.9-12 →

D2.Eco.2.9-12 C3 Framework

Use marginal benefits and marginal costs to construct an argument for or against an approach or solution to an economic issue.

How this material aligns: Students use marginal cost and benefit reasoning to build an argument for whichever rate structure best fits Calderwood's stated goals of fairness and conservation.

All materials for D2.Eco.2.9-12 →

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This material is in the public domain (CC0) and may be copied, edited, and shared freely, without attribution. Updated 2026-07-17.

Objectives

Students will calculate residential water bills under two different rate structures.
Students will analyze how a rate structure's design shifts costs among household types.
Students will argue for a rate option using cost-benefit reasoning.

Vocabulary

Revenue requirement: The total amount of money a utility must collect from customers each year to run the water system safely. Rates are set so that all the bills together add up to this amount.
Fixed charge: The part of a water bill that stays the same every month no matter how much water a family uses. It helps pay for the pipes, meters, and workers the utility needs even when no water is flowing.

Also: cost-of-service, uniform rate, increasing-block rate, volumetric charge, cross-subsidy

Teacher overview

A publicly owned water utility does not set prices to earn a profit; it sets them to collect exactly the money it needs to run, a total called the revenue requirement. How that total is split among customers is a policy choice with clear winners and losers. This lesson uses the fictional city of Calderwood to have students design and compare two rate structures, then defend one. A common student misconception is that a "fair" rate charges everyone the same price per gallon; the workshop shows that identical per-gallon pricing still distributes costs very differently once fixed charges and household size are considered.

Procedure

Hook (5 min): Ask students how their household would react if the water bill doubled next month, then reveal that a utility must collect its full revenue requirement no matter how it prices water. Post the guiding question: who should pay more when the total is fixed?

Direct instruction (15 min): Introduce the fictional city of Calderwood, whose water utility must collect a revenue requirement of $11.5 million per year from 20,000 households. Define fixed charge, volumetric charge, uniform rate, and increasing-block rate. Present the two candidate structures on the handout. Option A is a uniform rate: a fixed charge of $12 per month plus $6.00 per 1,000 gallons. Option B is an increasing-block rate: a fixed charge of $8 per month, then $4.00 per 1,000 gallons for the first 5,000 gallons and $10.00 per 1,000 gallons above 5,000. Work one bill on the board for a median household using 6,000 gallons. Under Option A the bill is $12 + (6 x $6.00) = $48. Under Option B it is $8 + (5 x $4.00) + (1 x $10.00) = $38.

Guided practice (15 min): In pairs, students compute the Option A and Option B bills for a low-use household of 3,000 gallons, then compare the two results and state in one sentence which structure charges the low user less.

Independent practice (15 min): Each student computes both bills for a high-use household of 15,000 gallons and records all six bills (low, median, high, under each option) in a table. They then write two sentences explaining who benefits and who pays more when the city switches from Option A to Option B.

Closure / exit ticket (5 min): On an index card, students answer: "Which option gives a bigger bill to a household using 15,000 gallons in the city of Calderwood, and by how much?" Collect and scan for the correct comparison before dismissal.

Designing Calderwood's Water Rates: A Cost-of-Service Workshop — Grade 12 Social Studies & Civics

Name: ____________________________ Date: ______________

Student Handout

Calderwood is a fictional city. Its water utility must collect a revenue requirement of $11.5 million per year from 20,000 households, and it is choosing between two rate structures:

Option A, a uniform rate: a fixed charge of $12 per month plus $6.00 per 1,000 gallons.
Option B, an increasing-block rate: a fixed charge of $8 per month, then $4.00 per 1,000 gallons for the first 5,000 gallons and $10.00 per 1,000 gallons above 5,000.

A low-use Calderwood household uses 3,000 gallons in a month. What is its bill under Option A?
What is that same low-use household's bill for 3,000 gallons under Option B?
By how many dollars do the two low-use bills for 3,000 gallons differ, and which option charges the low user less?
A high-use Calderwood household uses 15,000 gallons in a month. What is its bill under Option A?
What is that same high-use household's bill for 15,000 gallons under Option B?
The median household uses 6,000 gallons. Using all six bills (low use 3,000 gallons, median use 6,000 gallons, and high use 15,000 gallons under each option), explain in two sentences who benefits and who pays more when the city switches from Option A to Option B.
Exit ticket: Which option gives a bigger bill to a household using 15,000 gallons in the city of Calderwood, and by how much?

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: $30.
Guided practice (low use, 3,000 gallons): Option A is $12 + (3 x $6.00) = $30.
Answer: $20.
Option B is $8 + (3 x $4.00) = $20, since all 3,000 gallons fall inside the first block.
Answer: $10 (Option B charges the low user less).
Option B charges the low user $10 less because the first block is cheaper and the fixed charge is smaller.
Answer: $102.
Independent practice (high use, 15,000 gallons): Option A is $12 + (15 x $6.00) = $102.
Answer: $128.
Option B is $8 + (5 x $4.00) + (10 x $10.00) = $128.
Answer: Smaller households benefit and the largest user pays more.
The full table of six bills: low use $30 / $20, median use $48 / $38, high use $102 / $128. Option B lowers bills for smaller households and raises them for the largest user, shifting cost toward heavy use and rewarding conservation.
Answer: $26 (Option B is bigger).
Exit ticket: Option B gives the larger bill to the 15,000-gallon household, $128 versus $102, which is $26 more.

Differentiation

Support

Provide a partially completed bill table with the median-use column already filled in, and give a step-by-step worked card for the increasing-block calculation so students can focus on the comparison and the reasoning rather than the arithmetic.

Extension

Ask students to design a third rate structure that keeps a household using 3,000 gallons at or below the Option B bill while still charging the largest users more than Option A does, and to explain what goal their design prioritizes.

ELL supports

Pre-teach "fixed charge," "per 1,000 gallons," "block," and "revenue requirement" with a labeled sample bill. Provide sentence frames for the written comparison, such as "Option ___ charges the low-use household ___ because ___."

Extensions

Students can research how their own utility structures its residential rates, using only a bill or a published rate sheet a teacher provides, and classify it as uniform, increasing-block, or another structure, then explain which household types that choice favors.