Water for Schools
Menu

Lesson plan Grade 10 Health & Consumer Science

The Alvarado Family's Tiered Water Bill and the Affordability Line

A grade 10 consumer-math lesson: students compute a fictional household's tiered water and sewer bill, then test it against a widely used 4.5% affordability threshold.

Objectives

  1. Students will compute a tiered water-and-sewer bill by applying block rates and a fixed service charge.
  2. Students will express an annual bill as a percent of household income and compare it to an affordability threshold.

Vocabulary

Key words: tiered rate, block rate, fixed service charge, affordability threshold, consumption charge

Teacher overview

Most households pay for water on a tiered structure, where the price per thousand gallons rises as monthly use climbs, and a separate sewer charge is added on top. This lesson has students read a fictional utility's rate sheet and work out one month's full bill for the fictional Alvarado household, then annualize it and compare it to the roughly 4.5% of household income that a widely used rule of thumb, built from two EPA benchmarks, treats as a high burden. EPA has no single official cutoff. A common misconception this lesson addresses is that the whole bill is charged at the highest tier the household reaches; in a tiered system, only the gallons inside each block are charged at that block's rate.

Procedure

Hook (5 min): Project a blank bill showing a fixed charge, three usage tiers, and a sewer line. Ask students to predict, without calculating, whether a household that uses a little more water pays a little more or a lot more. Record predictions to revisit at closing.

Direct instruction (12 min): Walk through how a tiered, or block, rate works using the fictional Marisville Water District sheet. Model one block: if the first 3,000 gallons cost a set price per thousand, then only those gallons are charged at that rate, and the next gallons move into the next block. Show how the fixed service charge and the sewer charge, billed per thousand gallons of water used, are added last. Keep this an instructor-modeled example, not the graded work.

Guided practice (13 min): With the class, compute the water portion for a household that used exactly 5,000 gallons, so students see two blocks fill before independent work asks them to reach the third block. Check that every student labels units at each step.

Independent practice (15 min): Students complete the Student Handout for the fictional Alvarado household's 9,000-gallon month, working through each tier, the fixed and sewer charges, the monthly total, and the annual affordability percent.

Closure and exit ticket (5 min): Return to the hook prediction. On an index card, students answer: "In a tiered system, does moving from 6,000 to 9,000 gallons cost the same per thousand gallons as the first 3,000? Explain in one sentence." Collect and scan for correct understanding of block pricing.

The Alvarado Family's Tiered Water Bill and the Affordability Line — Grade 10 Health & Consumer Science
Name: ____________________________ Date: ______________

Student Handout

Use the fictional Marisville Water District residential rate sheet below for all questions. These figures are invented for this exercise.

  • Fixed monthly service charge: $18.00
  • Tier 1: first 3,000 gallons at $4.00 per 1,000 gallons
  • Tier 2: next 4,000 gallons (3,001 to 7,000) at $6.50 per 1,000 gallons
  • Tier 3: every gallon above 7,000 at $9.00 per 1,000 gallons
  • Sewer charge: $3.20 per 1,000 gallons of water used

The fictional Alvarado household used 9,000 gallons in July and reports a household income of $28,000 per year.

  1. How much is the Tier 1 charge for the first 3,000 gallons?
  2. How much is the Tier 2 charge for gallons 3,001 through 7,000?
  3. The household used 9,000 gallons, so 2,000 gallons fall into Tier 3. How much is the Tier 3 charge?
  4. Add the three tier charges to find the total water consumption charge.
  5. Add the $18.00 fixed service charge to the consumption charge to find the water portion of the bill.
  6. Find the sewer charge for 9,000 gallons at $3.20 per 1,000 gallons.
  7. Add the water portion and the sewer charge to find the total monthly bill.
  8. Multiply the monthly bill by 12 to estimate the annual cost, then find it as a percent of the $28,000 income. Is the household above or below the 4.5% high-burden threshold?

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

Answer Key

All values below refer to the fictional Marisville rate sheet and the fictional Alvarado household.

  1. Answer: $12.00.
    Tier 1 covers 3,000 gallons, which is 3 thousand-gallon units at $4.00 each: 3 x $4.00 = $12.00.
  2. Answer: $26.00.
    Tier 2 covers gallons 3,001 through 7,000, which is 4,000 gallons or 4 units at $6.50 each: 4 x $6.50 = $26.00.
  3. Answer: $18.00.
    Above 7,000 gallons the household used 9,000 - 7,000 = 2,000 gallons, or 2 units at $9.00 each: 2 x $9.00 = $18.00.
  4. Answer: $56.00.
    Total consumption charge is $12.00 + $26.00 + $18.00 = $56.00.
  5. Answer: $74.00.
    Water portion is the consumption charge plus the fixed charge: $56.00 + $18.00 = $74.00.
  6. Answer: $28.80.
    Sewer is billed on all 9,000 gallons: 9 units x $3.20 = $28.80.
  7. Answer: $102.80.
    Total monthly bill is the water portion plus sewer: $74.00 + $28.80 = $102.80.
  8. Answer: 4.41 percent (below the threshold).
    Annual cost is $102.80 x 12 = $1,233.60. As a share of income: $1,233.60 / $28,000 x 100 = 4.41 percent, which is just below the 4.5% high-burden line, though the margin is thin.

Differentiation

Support

Give these students a partially completed handout with Tiers 1 and 2 already worked, so they focus on the third tier, the sewer line, and the affordability percent. Provide a labeled worked example of a different household at 4,000 gallons to model block pricing before they begin.

Extension

Ask students to find the exact monthly use, in gallons, at which the Alvarado household's annual bill would reach 4.5 percent of the same income. They must set up the tiered charge as a function of gallons above 7,000 and solve, which requires reasoning backward through the block structure.

ELL supports

Pre-teach "tier," "block rate," "fixed charge," and "consumption" with a simple stacked-bar picture showing three price levels. Allow the exit-ticket explanation to be answered with a labeled diagram or a short phrase rather than a full sentence.

Extensions

Invite students to bring in a real water bill from home, with account numbers removed, and identify its fixed charge, its usage tiers, and its sewer line. Many utilities post their current rate sheets publicly, so a class can compare its own town's block structure to the fictional one used here.