Worksheet Grade 8 Science

The Okafor Household Water Audit: Flow Rates and Per-Person Use

A grade 8 science worksheet where a fictional family audits its water use: per-person demand, two showerhead flow rates as slopes, and toilet and leak losses.

Grade: Grade 8
Subject: Science
Material: Worksheet
Time: 40 min
Prep: No prep
Materials: calculator (optional), graph paper (optional)

Standards

MS-ESS3-4 NGSS

Construct an argument supported by evidence for how increases in human population and per-capita consumption of natural resources impact Earth's systems.

How this material aligns: Items 1, 2, and 10 have students use per-capita water-use evidence to argue how a growing population raises total demand on a town's reservoir and pipes.

All materials for MS-ESS3-4 →

8.EE.B.5 Common Core Math

Graph proportional relationships, interpreting the unit rate as the slope of the graph. Compare two different proportional relationships represented in different ways.

How this material aligns: Items 3 through 5 have students write two proportional flow equations and read each flow rate as the slope of a gallons-versus-minutes graph, then compare the slopes.

All materials for 8.EE.B.5 →

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This material is in the public domain (CC0) and may be copied, edited, and shared freely, without attribution. Updated 2026-07-23.

Objectives

Students will calculate per-person daily water use from a household total and compare it to typical values.
Students will model two showerhead flow rates as proportional equations and interpret each rate as a slope.
Students will argue how rising population increases total water demand on a shared supply.

Vocabulary

Flow rate: Flow rate measures how much water moves past a point in a certain amount of time, like gallons per minute through a garden hose. Bigger pipes and stronger pushes give bigger flow rates.
WaterSense: An EPA label on toilets, showerheads, faucets, and irrigation controllers that meet water-saving standards. It works like the ENERGY STAR label, but for water.

Also: per-capita use, slope, conservation

Teacher overview

A household water audit adds up where a family's water goes and looks for easy savings. This worksheet uses the fictional Okafor household to connect everyday fixtures to the mathematics of flow rates and per-person demand. Students model two showerheads as proportional relationships, read each flow rate as a slope, and then reason about what happens to a town's total demand as its population grows. A common misconception is that a lower flow rate saves no water because people shower longer to make up for it; the math shows that at the same shower length, the lower rate always uses fewer gallons.

The Okafor Household Water Audit: Flow Rates and Per-Person Use — Grade 8 Science

Name: ____________________________ Date: ______________

Student Worksheet

Use the following information about the fictional Okafor household for every item.

The Okafor household has 4 people and uses about 300 gallons of water per day, roughly 70 percent of it indoors. A standard showerhead flows at 2.5 gpm (gallons per minute); a water-saving WaterSense showerhead flows at 2.0 gpm. Typical per-person water use at home in the United States is often cited at 80 to 100 gallons per day. In a 2016 Water Research Foundation study of single-family homes, about 24 percent of indoor water went to flushing toilets. EPA WaterSense says a faucet that drips once per second can waste more than 3,000 gallons per year.

The Okafor household uses about 300 gallons per day and has 4 people. How many gallons per person per day does the household use?
Typical US per-person use at home is 80 to 100 gallons per day. Is the Okafor household above or below the low end of that range, and by how many gallons per person per day?
A standard showerhead flows at 2.5 gpm. Write an equation for the gallons g used during a shower that lasts m minutes with a standard showerhead.
A WaterSense showerhead flows at 2.0 gpm. Write the equation for the gallons g used during an m-minute shower with that showerhead.
On a graph of gallons (y) versus minutes (x), each flow rate is the slope of the line. Which showerhead gives the steeper line, and what does the steeper slope mean in terms of water use?
Using your equation from item 3, how many gallons does an 8-minute shower use with the standard 2.5 gpm showerhead?
Using your equation from item 4, how many gallons does an 8-minute shower use with the 2.0 gpm WaterSense showerhead?
How many gallons would each Okafor family member save per 8-minute shower by switching to the WaterSense showerhead?
The Okafor household uses about 70 percent of its 300 gallons indoors, which is 210 gallons per day. In the 2016 study, about 24 percent of indoor water went to toilets. Using that share, about how many gallons per day does the household use for flushing?
Suppose the Okafors' town doubles in population while per-person water use stays the same. Explain what happens to the town's total daily water demand and why that matters for its reservoir and pipes.
EPA WaterSense says a faucet dripping once per second can waste more than 3,000 gallons per year. Using 3,000 gallons per year, how many gallons would one such drip in the Okafor home waste over 2 years?

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: 75 gallons per person per day.
300 gallons ÷ 4 people = 75 gallons per person each day.
Answer: 5 gallons per person per day below.
The household's 75 gallons per person is below the low end of 80, by 80 − 75 = 5 gallons per person per day.
Answer: g = 2.5m.
At 2.5 gallons per minute, gallons used equals the rate times the number of minutes, so g = 2.5m.
Answer: g = 2.0m.
At 2.0 gallons per minute, the equation is g = 2.0m.
Answer: The standard 2.5 gpm showerhead gives the steeper line.
The standard showerhead has the larger flow rate, so its line rises faster; a steeper slope means more gallons are used for every added minute of showering.
Answer: 20 gallons. g = 2.5 × 8 = 20 gallons for an 8-minute standard shower.
Answer: 16 gallons. g = 2.0 × 8 = 16 gallons for an 8-minute WaterSense shower.
Answer: 4 gallons.
20 gallons − 16 gallons = 4 gallons saved per person for each 8-minute shower.
Answer: About 50 gallons per day.
210 gallons indoors × 0.24 = 50.4, or about 50 gallons per day used for flushing toilets.
Answer: Total demand doubles.
If the number of people doubles and each person still uses the same amount, the town's total daily demand doubles, which draws more water from the reservoir and pushes more water through pipes that were sized for a smaller population.
Answer: 6,000 gallons.
3,000 gallons per year × 2 years = 6,000 gallons wasted by one steady drip over two years. The actual amount depends on how large each drip is.

Differentiation

Support (below grade level)

Give students a completed table of gallons used at 0, 2, 4, 6, and 8 minutes for both showerheads so they can see each proportional pattern before writing the equations in items 3 and 4. Allow a calculator for every calculation.

Extension (above grade level)

Ask students to find the shower length at which a standard 2.5 gpm showerhead would use the same 16 gallons that an 8-minute WaterSense shower uses, and to explain what that result shows about trading a shorter shower for a higher flow rate.

ELL supports

Pre-teach "flow rate," "per person," and "slope" using a picture of water filling a bucket, with a faster and a slower tap. Provide sentence starters for items 5 and 10, such as "The steeper line means the household uses ___ because ___."

Extensions

Have students total the Okafor household's yearly shower water for both showerheads, assuming each of the 4 people takes one 8-minute shower a day, and compare the two yearly totals to show how a small per-shower saving adds up across a family and a year.