Water Quality: How is it Measured?

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SWBAT describe different tests used in determining water quality and what those tests tell us about the tested water sample.

Big Idea

Water quality is determined by understanding many characteristics of a water sample, which we learn through various chemical and biological tests.

Why This Lesson?

This lesson allows students to explore the different tests involved in evaluating water quality before they will be performing those tests (Water Quality: Testing Samples) on real world water samples collected by student volunteers.

Evaluating water samples and exploring sources of poor quality water will help students meet Performance Expectation HS-ESS3-6: Use a computational representation to illustrate the relationships among Earth systems and how those relationships are being modified due to human activity.  Students will be gathering information and sharing it with each other, therefore engaging in SEP 8: Obtaining, Evaluating, and Communicating Information.


5 minutes

While I take attendance, students do a warm-up activity in their composition Warm-Up/Reflection books.  I use warm-ups to either probe for students' prior knowledge about the day's upcoming lesson or to have them bring to mind and review what they should have learned previously.  (To read more about Warm Up and Reflection Books please see the attached resource.)

Today’s Warm-Up: “How do we know water quality is good or bad?”

In this case, the warm-up is asking students to draw upon their prior knowledge to think about practical uses of chemistry as it applies to testing water quality.  It is also preparing students for today's activity during which they will be learning about all of the components considered in measuring water quality.  Tomorrow's lesson will involve actual testing of various water samples to determine their water quality.

If time permits, I walk around with a self-inking stamp to stamp the completed warm-ups indicating participation, but not necessarily accuracy.  In order to speed things up, my students have been trained to pass their books into the center of the table rows and stack them so that I can quickly pass by and stamp.  On days when there is too much business keeping, I do not stamp.  Students have been told that warm-ups are occasionally immediately checked and other times not.  At the end of each unit, Warm-Up/Reflection Books are collected and spot-checked.  Today, I do stamp books.  We do not discuss answers to the pre-lab question because students will discover the answer during today's activity.

Introduction to Jigsaw Activity

10 minutes

I begin by numbering my students off, 1 through 9, because there are nine different water quality tests that we will be examining.  The tests that are assigned to each group are listed below:

  1. Dissolved oxygen
  2. Fecal coliform
  3. pH
  4. Biochemical oxygen demand
  5. Temperature
  6. Phosphate
  7. Nitrate
  8. Turbidity 
  9. Total solids

For this activity, I use the Water Quality Index (WQI) Field Trip Kit available from Flinn Scientific, Inc.  

I give my students specific areas 1-9 to gather in small groups before handing out the descriptions of each water quality test, and ask them to move.  I previously photocopied each individual test description from the handbook included in the WQI kit.  Each student gets a copy of their specific test to read and understand.  

I explain that each student is going to be responsible for becoming an expert on one water quality test.  I also explain that after they have 10 minutes to become experts on their test, they will need to share their information and gather the information about the other eight tests from their peers.  Then, I hand out the Water Quality Jigsaw Activity - individual topics to each student to help organize their test's information.

Jigsaw Activity: Becoming an Expert

10 minutes

Students read about the individual water quality test that they were assigned.  They complete their handout answering the questions:

  • What does this test tell us?
  • Why is it important?
  • How does it relate to water quality?
  • How is this test performed?

As students work, I move around the room answering questions and encouraging students to be talking to each other in their small expert groups.

Jigsaw Activity: Sharing Information

25 minutes

Once students have gathered the information about their individual water quality tests, it is time to share their findings.  I begin by handing out Water Quality Table.  Students will record information for each water quality test, including what it tells us, how it relates to water quality, and how the test is performed.

I explain to students that they should find a couple of students who are experts on different tests and work together in threes or fours sharing their findings.  They should continue sharing with other students until they can complete their Water Quality table handout.


Sample Student Work:



Student Reflection

5 minutes

In student's Warm-Up/Reflection Books, students should spend about 3-5 minutes writing a response to the day's reflection prompt.  Prompts are designed to either help students focus on key learning goals from the day's lesson or to prompt deeper thinking.  The responses also allow me to see if there are any students who are missing the mark in terms of understanding.  The collection of responses in the composition books can also show a progression (or lack thereof) for individual students. 

Today, I ask students to instead of recording their answers in their books, to record their answers on their activity handouts, simply because we were pressed for time.

Today's Reflection Prompt:  "Why are there multiple tests to consider when judging water quality?”

Desired student responses should indicate that each test measures a different characteristic of the water sample, and that all test results together give a clearer picture of the overall quality of the water.  During student sharing of their individual tests that they had been assigned, the discussion coming from students was rich.  In the beginning, the discussions were very simple and centered around accomplishing the task of filling in the table.  But by the end of class, the discussions had changed and students were asking each other follow up questions--they were particularly fascinated by the Secchi disk and passed it around as the "turbidity" experts tried to demonstrate how it would work.

Most students could easily articulate that there are multiple tests because each test focuses on a different characteristic of the sample.  All of these characteristics become important when deciding water purity.