Classroom activity Grade 7 Health & Consumer Science
Bottled or Tap? A Gullhaven Cost-Per-Gallon Comparison
A grade 7 activity where teams compute the cost per gallon of bottled water versus tap and weigh cost, quality, and waste for a fictional school.
Objectives
- Students will compute the cost per gallon of tap and bottled water.
- Students will find how many times more bottled water costs than tap.
- Students will weigh cost, quality, and plastic waste to make a recommendation.
Vocabulary
Key words: cost per gallon, bottled water, tap water, single-use
Teacher overview
This is a team challenge for groups of three or four students who act as advisors to a fictional school. Each team gets a price card for bottled water and the local tap-water rate for the town of Gullhaven, then computes the cost per gallon of each source. Teams use their numbers to compare the cost of supplying a school sports day two ways, and they finish by weighing cost, water quality, and plastic waste to make a recommendation. The activity shows that tap water from the utility, which must meet federal and state drinking water rules, is far cheaper per gallon than bottled water, so the comparison rests on real arithmetic rather than opinion.
Activity Directions
- Seat students in teams of three or four. Give each team a price card that reads: bottled water costs $1.20 per gallon at the store, and Gullhaven tap water costs $5.00 per 1,000 gallons. Explain that all prices are fictional but realistic.
- Task one: teams compute the cost of one gallon of Gullhaven tap water by dividing $5.00 by 1,000. Circulate and confirm each team reaches half a cent per gallon before moving on.
- Task two: teams compute how many times more expensive one gallon of bottled water is than one gallon of tap water, dividing the bottled price by the tap price.
- Task three: the school plans a sports day where the community will drink about 500 gallons of water. Teams compute the cost of supplying it entirely from tap and entirely from bottled water.
- Task four: teams find how much the school would save by filling reusable bottles at the fountain instead of buying bottled water for the sports day.
- Task five: assuming each gallon of bottled water uses about 8 single-use bottles, teams compute how many bottles the school would avoid by using tap water.
- On poster paper, each team writes its cost-per-gallon results and a one-sentence recommendation to the school, naming cost, quality, and plastic waste.
- End the activity with a short gallery walk of the posters, then hold the debrief below.
Student Handout
Record your team's answer to each numbered question on your poster. Use the two prices from the town of Gullhaven's price card: bottled water costs $1.20 per gallon, and tap water costs $5.00 per 1,000 gallons. The sports day will use about 500 gallons of water, and each gallon of bottled water uses about 8 single-use bottles.
- Find the cost of one gallon of Gullhaven tap water by dividing $5.00 by 1,000 gallons.
- Using your answer to question 1, find how many times more one gallon of bottled water costs than one gallon of tap water.
- Find the total cost of supplying all 500 gallons of the sports day from tap water, and then the total cost of supplying all 500 gallons from bottled water.
- Find how much the school would save on the sports day by filling reusable bottles at the fountain instead of buying bottled water.
- Find how many single-use bottles the school would avoid by supplying the 500 gallons from tap water instead of bottled water.
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: $0.005 per gallon. $5.00 divided by 1,000 gallons is half a cent per gallon.
- Answer: 240 times. $1.20 divided by $0.005 is 240, so bottled water costs 240 times as much per gallon.
- Answer: $2.50 from tap and $600.00 from bottled. 500 gallons times $0.005 is $2.50; 500 gallons times $1.20 is $600.00.
- Answer: $597.50 saved. $600.00 minus $2.50 is $597.50 saved by using the fountain.
- Answer: 4,000 bottles. 500 gallons times about 8 bottles per gallon is 4,000 single-use bottles avoided.
- Debrief question: "Besides cost, why might a school still choose tap water?" Answer: Tap water must meet federal and state drinking water rules and is tested regularly by the utility, and using the fountain avoids thousands of single-use bottles, so tap water also comes with known, regulated quality and cuts plastic waste.
Differentiation
Support
Give these teams the tap cost per gallon already computed, so they start from task two. Provide a labeled reminder that "per 1,000 gallons" means dividing the price by 1,000 to get one gallon.
Extension
Ask a team to find the yearly savings if the school avoids buying bottled water on 30 sports days, and to express the bottled cost as a percent of the tap cost for a single sports day.
ELL supports
Pre-teach "cost per gallon," "bottled," and "single-use" with real objects: a reusable bottle and a disposable one. Provide a sentence frame for the recommendation: "The school should use ___ because it costs ___ and avoids ___."