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Worksheet Grade 7 Health & Consumer Science

Choosing a Home Water Filter for the Delacroix Family

A grade 7 consumer worksheet comparing three home water filters by cost per gallon and what they remove, including PFAS, for a fictional family.

Objectives

  1. Students will find how many filter replacements a set water use requires in a year.
  2. Students will compute first-year filter costs and cost per gallon.
  3. Students will weigh cost against which filter reduces PFAS to make a consumer choice.

Vocabulary

Reverse osmosis
Reverse osmosis cleans water by pushing it through a membrane with holes so tiny that salt and most other dissolved things cannot fit through. It can even turn seawater into fresh water.
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.

Also: filter, cost per gallon

Teacher overview

Home water filters range from a cheap pitcher to an under-sink reverse-osmosis unit, and the right choice depends on both cost and what the filter can remove. This worksheet gives students a fictional price list for the Delacroix family and asks them to compare three filters by yearly cost and cost per gallon. Only the reverse-osmosis option reduces PFAS, so students weigh price against protection to make a real consumer decision.

Choosing a Home Water Filter for the Delacroix Family — Grade 7 Health & Consumer Science
Name: ____________________________ Date: ______________

Student Worksheet

Use this fictional price list. The Delacroix family uses about 730 gallons of drinking and cooking water each year.

Option Upfront cost Replacement cost Gallons per replacement Reduces PFAS?
A: pitcher filter $35 $8 40 No
B: faucet-mount filter $45 $15 100 No
C: under-sink reverse osmosis $220 $60 1,000 Yes

The federal limit for two common PFAS chemicals is 4 parts per trillion each. Only Option C reduces PFAS.

  1. Option A's pitcher cartridge lasts 40 gallons. How many cartridges does 730 gallons of use need in a year? Round up to a whole cartridge.
  2. What is Option A's replacement cost for the first year, using your answer from item 1?
  3. Option B's cartridge lasts 100 gallons. How many cartridges does 730 gallons need in a year? Round up.
  4. What is Option B's replacement cost for the first year?
  5. Option C's membrane lasts 1,000 gallons. How many membranes does 730 gallons need in a year? Round up.
  6. What is Option C's replacement cost for the first year?
  7. Find Option C's first-year total cost by adding its $220 upfront cost to its membrane cost from item 6.
  8. Find Option A's cost per gallon for the year: divide its first-year replacement cost by 730 gallons. Round to the nearest cent.
  9. The federal limit for two common PFAS chemicals is 4 parts per trillion each. In one sentence, explain why a family whose well tests above that limit might still choose Option C even though it costs the most upfront.
  10. Find the first-year total cost for Options A and B, then state which of the three options has the lowest first-year total cost and which is the only one that reduces PFAS.

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: 19 cartridges. 730 gallons divided by 40 gallons is 18.25, which rounds up to 19 cartridges.
  2. Answer: $152. 19 cartridges times $8 each is $152.
  3. Answer: 8 cartridges. 730 gallons divided by 100 gallons is 7.3, which rounds up to 8 cartridges.
  4. Answer: $120. 8 cartridges times $15 each is $120.
  5. Answer: 1 membrane. 730 gallons divided by 1,000 gallons is 0.73, which rounds up to 1 membrane.
  6. Answer: $60. 1 membrane times $60 is $60.
  7. Answer: $280. The $220 upfront cost plus the $60 membrane cost is $280.
  8. Answer: $0.21 per gallon. $152 divided by 730 gallons is about $0.208, which rounds to $0.21 per gallon.
  9. Answer: Only Option C reduces PFAS, so a family whose well is over the limit needs it to lower the chemicals even though it costs more at first.
  10. Answer: Option B has the lowest first-year total. Option A totals $35 plus $152, or $187; Option B totals $45 plus $120, or $165; Option C totals $280. Option C is the only one that reduces PFAS.

Differentiation

Support

Provide the first row worked through as a model, and a labeled reminder that "round up" means any leftover gallons still need one more cartridge. Allow calculators throughout.

Extension

Ask students to find how many years it would take for Option C's lower yearly replacement cost to make up for its higher upfront cost compared with Option B, showing their reasoning.

ELL supports

Pre-teach "filter," "cartridge," "membrane," and "reduce" with simple pictures. Provide a sentence frame for item 9: "A family over the limit might choose Option C because ___."