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Lesson plan Grade 11 Health & Consumer Science

Choosing a PFAS Filter for the Novak Household in Verde Mesa

A grade 11 health lesson where students weigh a PFAS filter for a fictional household, comparing tap readings to the 4.0 ppt federal limit and two filters' yearly costs.

Objectives

  1. Students will compare a household's PFAS readings to the federal maximum contaminant level.
  2. Students will build and compare cost equations for two point-of-use filter options.
  3. Students will explain how a contaminant limit can be in force while its deadline may shift.

Vocabulary

PFAS
A large family of human-made chemicals used in things like nonstick pans, waterproof fabric, and firefighting foam. They are called forever chemicals because they take a very long time to break down.
Maximum contaminant level (MCL)
A maximum contaminant level, or MCL, is the highest amount of a certain substance that federal rules allow in drinking water. Water systems test regularly to prove their water stays under each limit.
Parts per trillion
A unit for measuring extremely small amounts of a chemical in water. PFAS limits are set in parts per trillion because these chemicals matter even in tiny doses.
Point-of-use filter
A small filter at a single faucet, like a pitcher filter or one that attaches to the tap. Certified filters can remove lead or PFAS from the water a family drinks.

Also: compliance deadline

Teacher overview

PFAS, a family of long-lasting synthetic chemicals, moved from an unregulated contaminant to a regulated one in 2024, when EPA set a maximum contaminant level of 4.0 parts per trillion each for PFOA and PFOS. The rule is still in motion: in May 2026 EPA proposed letting eligible utilities apply for a two-year exemption that would move their deadline from 2029 to 2031 (not final as of September 2026), so a household reading its water quality report today has to decide whether to wait for its utility or act on its own. In this lesson students step into that decision for the fictional Novak household in the equally fictional town of Verde Mesa, comparing tap readings to the limit and weighing the cost of two filters. A common misconception this lesson addresses is that any detectable PFAS means the tap water is illegal to drink; the regulation sets a specific numeric limit and a phased compliance timeline rather than a zero-tolerance ban.

Procedure

Hook (5 min): Ask students where they think the water in a plastic bottle and the water from a home tap are each tested for PFAS, and who is responsible for fixing a problem when a contaminant is found. Record ideas, then explain that public tap water now has an enforceable PFAS limit that utilities are phasing in.

Direct instruction (12 min): Introduce PFAS, the 4.0 parts per trillion limit for PFOA and PFOS, and the proposal to let eligible utilities apply for more time, from 2029 to 2031. Stress that "regulation in motion" means the limit is set even though the deadline for some utilities may move.

Model a cost comparison (10 min): Using a fictional sample filter that costs 200 dollars up front plus 60 dollars a year in cartridges, model the total-cost equation on the board: C = 200 + 60y, and evaluate it at y = 2 to get 320 dollars. Show how writing cost as an equation lets students compare options at any number of years rather than guessing.

Independent practice (15 min): Students complete the handout for the Novak household, comparing the tap readings to the limit, building cost equations for two real-world-style filter choices, and finding the year at which the two options cost the same. Circulate to confirm students set the two equations equal in item 7 rather than comparing single years only.

Formative check and close (8 min): Exit ticket on a card: "The Novak household's utility may apply for an exemption that would give it until 2031 to meet the PFAS limit. Give one reason a family might filter now and one reason a family might wait." Scan responses to confirm students can reason about a deadline that may shift rather than treating the limit as immediate.

Choosing a PFAS Filter for the Novak Household in Verde Mesa — Grade 11 Health & Consumer Science
Name: ____________________________ Date: ______________

Student Handout

A test of the Novak household's tap water in the fictional town of Verde Mesa found these results, which the family compares with the federal maximum contaminant level (MCL) of 4.0 parts per trillion (ppt) each for PFOA and PFOS:

  • PFOA: 6.2 ppt
  • PFOS: 3.1 ppt

Two certified point-of-use filters are available to the fictional household:

  • Under-sink filter: 240 dollars to install, plus 90 dollars per year in replacement cartridges.
  • Pitcher filter: 45 dollars up front, plus 120 dollars per year in cartridges.
  1. By how many ppt does the PFOA reading of 6.2 ppt exceed its 4.0 ppt MCL?
  2. What percent of the 4.0 ppt MCL is the 6.2 ppt PFOA reading? Round to the nearest whole percent.
  3. Is the PFOS reading of 3.1 ppt above or below its 4.0 ppt MCL, and by how much?
  4. Write an equation for the under-sink filter's total cost U after y years, then find the cost after 3 years.
  5. Write an equation for the pitcher filter's total cost P after y years, then find the cost after 3 years.
  6. Over 3 years, which filter costs less, and by how much?
  7. Set your two equations equal and solve for the year y at which the two filters cost the same amount.
  8. EPA set the PFOA and PFOS limit in 2024 but in May 2026 proposed letting eligible utilities apply for an exemption that would move their compliance deadline from 2029 to 2031. Explain why the Novak household might install a filter now rather than wait for the utility to comply.

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: 2.2 ppt. 6.2 ppt minus the 4.0 ppt MCL equals 2.2 ppt above the limit.
  2. Answer: 155%. 6.2 divided by 4.0 equals 1.55, or 155% of the MCL.
  3. Answer: Below, by 0.9 ppt. 4.0 ppt minus 3.1 ppt equals 0.9 ppt, so PFOS is under its limit.
  4. Answer: 510 dollars. U = 240 + 90y; at y = 3, U = 240 + 270 = 510 dollars.
  5. Answer: 405 dollars. P = 45 + 120y; at y = 3, P = 45 + 360 = 405 dollars.
  6. Answer: The pitcher, by 105 dollars. After 3 years the pitcher costs 405 dollars and the under-sink costs 510 dollars, a 105-dollar difference.
  7. Answer: 6.5 years. Setting 240 + 90y = 45 + 120y gives 195 = 30y, so y = 6.5 years; beyond that point the under-sink filter is cheaper.
  8. Answer: Accept any answer noting that the enforceable limit already identifies a health-based concern, that the household's own PFOA reading exceeds the limit now, and that waiting until as late as 2031 means several more years of exposure the family could reduce today with a certified filter.

Differentiation

Support

Provide the two cost equations already set up in items 4 and 5, leaving students to evaluate them and to solve the break-even equation in item 7. Offer a filled example of "percent of the limit" using a different reading before students attempt item 2.

Extension

Ask students to add a third option, a whole-house filter costing 900 dollars up front plus 40 dollars per year, write its cost equation, and determine the range of years over which each of the three options is the cheapest choice for the fictional household.

ELL supports

Pre-teach "contaminant," "limit," "cartridge," and "deadline" with simple definitions and an icon set. Provide a two-column frame labeled "filter now" and "wait" for item 8 so students can list reasons before writing them in full sentences.