Worksheet Grade 6 Science

Selby Point's Reverse Osmosis Unit: Recovery and Reject Water

A grade 6 science worksheet on a fictional reverse osmosis unit, where students find recovery percent and how much feed water becomes clean water instead of reject.

Grade: Grade 6
Subject: Science
Material: Worksheet
Time: 30 min
Prep: No prep
Materials: Calculator

Standards

6.RP.A.1 Common Core Math

Understand the concept of a ratio and use ratio language to describe a ratio relationship between two quantities. For example, 'The ratio of wings to beaks in the bird house at the zoo was 2:1, because for every 2 wings there was 1 beak.'

How this material aligns: Items 4 and 7 describe the ratio of clean water to feed water and to reject water, the ratio-language reasoning 6.RP.A.1 asks students to use and interpret.

All materials for 6.RP.A.1 →

6.RP.A.3 Common Core Math

Use ratio and rate reasoning to solve real-world and mathematical problems, e.g., by reasoning about tables of equivalent ratios, tape diagrams, double number line diagrams, or equations, including finding a percent of a quantity and converting measurement units.

How this material aligns: Items 2, 3, 5, and 8 find recovery as a percent of feed water and use that percent to predict clean-water output, the percent and ratio work 6.RP.A.3 targets.

All materials for 6.RP.A.3 →

MS-ESS3-3 NGSS

Apply scientific principles to design a method for monitoring and minimizing a human impact on the environment.

How this material aligns: Items 1, 6, 9, and 10 quantify the reject water the unit sends to waste and ask why operators want higher recovery, weighing that water-use cost the way this standard's monitor-and-minimize design work requires.

All materials for MS-ESS3-3 →

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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 find recovery as the percent of feed water that becomes clean water.
Students will use a recovery percent to predict how much clean water and reject water a run produces.

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.

Also: membrane, recovery, reject

Teacher overview

Reverse osmosis cleans water by pushing it through a thin sheet called a membrane. The membrane lets clean water through and holds salts and other bits back. The clean water that passes through is what the plant keeps, and the leftover salty water is the reject. This worksheet has students track those two streams at Selby Point, a fictional water plant, and find what percent of the incoming water ends up clean. A common error is dividing the clean water by the reject instead of by the total feed water; recovery is always a share of the feed, not of the reject.

Selby Point's Reverse Osmosis Unit: Recovery and Reject Water — Grade 6 Science

Name: ____________________________ Date: ______________

Student Worksheet

Selby Point runs a fictional reverse osmosis unit. The water that goes in is called feed water. Recovery is the percent of the feed water that comes out clean. Use these facts for every problem.

Recovery percent = clean water divided by feed water, times 100.
Run 1: the unit takes in 500 gallons of feed water and makes 300 gallons of clean water.

In Run 1, the reject is the feed water that did not become clean. How many gallons of reject does Run 1 make?
Find the recovery percent for Run 1.
What percent of the feed water becomes reject in Run 1?
Write the ratio of clean water to reject water in Run 1 in simplest form.
In Run 2, the unit takes in 800 gallons of feed water and runs at the same 60 percent recovery. How many gallons of clean water does it make?
How many gallons of reject does Run 2 make?
The recovery percent and the reject percent are two parts of the same feed water. What must they always add up to? Explain in one sentence.
The unit runs three batches, each with 500 gallons of feed water at 60 percent recovery. How many gallons of clean water do the three batches make in all?
In one or two sentences, explain why operators would want a higher recovery percent rather than a lower one.
The salts held back by the membrane leave in the reject water. Explain what that means for how salty the reject is compared with the feed 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: 200 gallons.
500 gallons of feed minus 300 gallons of clean water = 200 gallons of reject.
Answer: 60 percent.
300 gallons divided by 500 gallons = 0.6, times 100 = 60 percent.
Answer: 40 percent.
200 gallons of reject divided by 500 gallons of feed = 0.4, times 100 = 40 percent.
Answer: 3 to 2.
Clean water to reject is 300 to 200. Both divide by 100 to give 3 to 2.
Answer: 480 gallons.
60 percent of 800 gallons = 0.6 times 800 = 480 gallons of clean water.
Answer: 320 gallons.
800 gallons of feed minus 480 gallons of clean water = 320 gallons of reject.
Answer: 100 percent.
The clean share and the reject share are the two parts of all the feed water, so together they must equal 100 percent of it.
Answer: 900 gallons.
Each batch makes 60 percent of 500 = 300 gallons of clean water. Three batches make 3 times 300 = 900 gallons.
Answer: A higher recovery percent means more of the feed water becomes clean water and less is thrown away as reject. That wastes less water and gets more usable water from each gallon pumped in.
Answer: The membrane holds the salts back, so the salts pile up in the smaller amount of reject water. That makes the reject saltier than the feed water it came from.

Differentiation

Support

Provide a simple two-box diagram labeled "feed water in," "clean water out," and "reject out," and fill in Run 1's numbers together before students start. Give the recovery formula on a card and let students use a calculator, and remind them the bottom of the fraction is always the feed water.

Extension

Ask students to find the feed water a run would need in order to make exactly 600 gallons of clean water at 60 percent recovery, and to show the work that leads to their answer.

ELL supports

Pre-teach "membrane," "recovery," and "reject" with a picture of water passing through a filter sheet, clean water going one way and salty water the other. Provide the frame "Recovery is the part of the feed water that comes out ___," and allow short-phrase answers for items 7, 9, and 10.