Separating Mixtures: Follow up

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Students will be able to analyze the reasoning behind using wastewater as drinking water and the safety of the engineering behind this idea.

Big Idea

Is wastewater safe to drink?

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Purpose of Lesson:

The purpose of this lesson is to dig more deeply into the reasoning and safety behind using treated waste water.

Major Strategies to Watch for:

1) Rigorous reading assignment

2) Analysis of a variety of texts (reading, video, audio)

3) Socratic Seminar


3 minutes

Learning Goal: Analyze the reasoning behind using waste water for drinking water and the safety of this choice.

Opening Question: Is treated waste water safe for people to drink?  Why or why not?

Students record their opening question on their learning goal sheet and are ready to start class 3 min after the bell has rung.  I reward students who get started early with ROCK STAR SCIENTIST tickets.  

This question tends to be a topic that students have a lot to say about.  Once they understand that treated wastewater came from sinks and toilets, they generally have strong opinions on whether it should be used as drinking water or not.  This is a great opportunity for an open class discussion.

Follow the links to learn more about the beginning of class strategies and ROCK STAR scientist tickets


5 minutes

I love the Bill Gates Drinks Human Waste Converted Drinking Water, Would You? video because it shows a rich powerful man drinking water that was made from toilet sludge. I like to show this because it might influence their decisions about safety and allow them to overcome the "gross" factor that we saw yesterday in students' writings. 

After the video, I ask students how it influenced their thinking and whether it changed their minds.

Focus and Independent Work

20 minutes

The purpose of this section is to help the students understand how to do the Wastewater Reading task today and to model it for them. Today the students will be using their wastewater annotations from yesterday to answer questions.

The strategy that I want to use to push the students back to the text comes from Fisher and Frey's book RIGOROUS READING. In this strategy, students mark  the question number by the evidence in the text that they used. This forces the students to actually use evidence from the reading rather than just answer from their heads. This is especially good for gifted readers.  

People who are gifted readers often read so fast and make some many connections and inferences without thinking that they cannot specifically point to evidence in the reading. This can cause problems later on as students are using evidence in a Claim, Evidence, Reasoning writing.  

Below is a video of this focus lesson.  

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Once the students understand the process, I release them to work independently. I like to project an online timer onto my SMARTBoard so that students can manage their own time and know when the activity will end.  For this activity I would give 10-15 min. When the online timer goes off, I ask students to compare their answers to questions 1, 2 and 3 with their partners. My hope during their conversations is that they will see similarities in the way they answered but also be able to see that different people interpret readings and information in different ways.  


10 minutes

The purpose of this section is to build the understanding of how treated wastewater can be beneficial when water is short. The Water, The World Water Crisis video does a superb job at showing the importance of clean water in our lives and telling the stories of people that are living without clean water.  

Before the video I ask the students to watch the video to find out:


  1. Why is water so important?
  2. Why is water scarce in some places?
  3. How can unclean water affect lives? 

After the video I ask students if they can think of other options besides using waste water. Often students' answers range from using sea water and bring water from something else. Desalination is  one of the methods of getting a great water supply that also involves separating substances.  

Will Turning Seawater Into Drinking Water Help Drought-Hit California? (NPR article) discusses some of the benefits and challenges of using desalination. I introduce this story to students telling them they are going to here about using desalination to help solve the water problem in California. I ask the students to listen to the story for pros and cons of using desalination.

After the story, I write the words pros and cons on the board. I have students shout out the facts that they heard from the story. If there are things they don't remember I point them out.  

This is our list from one class.




10 minutes

In this section, I open a socratic seminar type lesson to have an open discussion about what the best way to get clean water for drought stricken areas is.  I have students move to a circle and I open with a question- What's the best way to get clean water for people?  

A Socratic Seminar is a discussion format where students build off of each other's answers.  The point is for the teacher to be a facilitator asking questions at the right time and pushing the conversation to new places but for the students to be the ones talking and thinking.  It is also important for students to use information from the text to support their ideas.  In this situation students have a reading, video, and news story to draw ideas from.  During the Socratic Seminar I use my phone or table to score the student responses on Class Dojo.  This allows me to keep track of who is talking and what they are saying.  At the end of the seminar I show the students the points, but I often don't actually put them in the grade book.  The purpose of the points is simply to show students how they could contribute more to the conversation rather than to evaluate them. You can read more about Socratic Seminars here.  


2 minutes

Closing Statement: Today we learning about why treated wastewater might be an important resource and analyzed the overall safety of the procedure. 

Closing Question: How could treated waste water help people? 

Closure depends greatly on timing and is not as easy to plan in advance as opening.  You can find more information about how I manage closure here.