Water and Global Responsibility STEM UnitLP14_Water Quality Testing

Lesson Plan 14: Water Quality Testing

Overview

This lesson exposes students to three forms of water quality testing to give them an understanding of how we determine whether water is safe to drink.

Background Knowledge

Students should have an understanding of:

  • Basic chemistry skills
  • Difference between safe and unsafe water
  • Where their water comes from and how it is treated

Educators may want to review the backgrounder at the end of the lesson plan on water quality testing prior to the lesson.

Time Required:1.5 hrs

Grade Level: Grades 5 and 6

Subject Area: Science, Social Studies, Math

Key Words: Turbidity

Alberta Curriculum Links:See curriculum link table

Lesson Plan 14: Water Quality Testing 1 hr

Learning Expectations

  1. Describe different forms of water quality testing.
  2. Discuss the importance of water quality testing.

Materials

□Power Point on Water Quality Testing

□LCD Projector

Turbidity Test

□Turbidity tube

□1 sample of tap water

□1 sample of dirty water

pH Test

□Ph Strips

□1 labeled Beaker of each of the following:

a)Lemon Juice

b)Vinegar

c)Milk of Magnesia

d)Salt water

e)Tap water

f)Ammonia

g)Swamp or dirty water

Dissolved oxygen test

□Dissolved oxygen tablets

□1 beaker of tap water

□1 beaker of dirty water

□Refills of each type of sample water

Intro Demonstration

□1 glass of tap water

□1 glass of clear water with white vinegar

□1 glass of dirty water

□Numbered cards to set beside the water classes.

More than one station for each type of test may be required depending on group size.

Preparation

□Prepare LCD Projector with Water Quality Testing PowerPoint.

□Set up three glasses at the front of the class: 1 glass of tap water, 1 glass of tap water with white vinegar, and 1 glass of dirty water.

□Number the glasses from 1 to 3. The numbers should be visible from the back of the class.

□Label beakers used for pH tests.

□Set-up up at least one station for each test. You may want to do more depending on class size.

Introduction20 minutes

  1. Direct students attention to the three glasses of water at the front of the room.
  2. Ask student to vote on which of the glasses they would drink from and why. Tabulate and record their results.
  3. Ask three volunteers to come to the front of the room and examine the water glasses.
  4. Ask them what glass of water they would drink and tell them to explain why.
  5. Draw students attention to the reasoning behind why the students chose a particular glass of water: it’s clear, it has no smell, no taste etc.
  6. Explain that there are many things that we can see, smell and taste in water that can indicate if it might be safe to drink. This is called physical testing.
  7. Tell students that to be certain that water is safe there are certain tests that we need to perform to detect things in the water that we can’t always sense
  8. Explain that today they are going to see three types of tests: turbidity, ph, and dissolved oxygen.

Water Quality Testing Power Point 20 minutes

  1. Go through the PowerPoint provided on water quality testing.
  2. Do an example of each of the tests that they will conduct: turbidity, pH and dissolved oxygen.

Testing45 minutes

  1. Divide students into groups of 3 to 4 and send each group to a testing station.
  2. Ask each group to perform the test at the station and record their results on the handout provided (see the end of the lesson).
  3. When they have completed the test, ask them to rotate to the next station. They will need to rotate three times to complete each test.
  4. Ask groups to report their results for each test.
  5. Discuss any differences between the groups.

Review 30 minutes

  1. Ask students to write down the procedures for each type of test, and then respond to the following question in their journal. “With regards to water quality testing I was surprisedabout. . . .”

Resources:

  • The Safe Drinking Water Foundation in Saskatchewan provides water quality testing kits for students:
  • Kits can also be obtained from: . At this site you’ll also discover how your class can become involved in World Water Monitoring Day.
  • You may also be able to purchase the materials required for these tests through your science lead or school supplies.
  • Read the backgrounder provided on water quality testing

Backgrounder on Water Quality Testing

Turbidity

Turbidity is a physical property of water. It is the ‘cloudiness’ caused by small particles that are generally invisible to the naked eye. One can compare it to smoke in the air. In rivers and other surface waters, turbidity usually increases after heavy rain as the water picks up dirt particles.

The units for measuring turbidity are NTU (Nephelometric Turbidity Units) which are not concentrations (mg per L), but rather values associated with how much light is reflected due to the amount of particles in the water. The more particles, the higher the NTU value.

Potential Health Effects

Turbidity doesn’t cause direct health impacts but is an indicator of biological contamination, because viruses, parasites and bacteria like to attach themselves to small particles. Turbidity also reduces the effectiveness of chlorination as chlorine. The chlorine combineswith the particles and leaves less chlorine available to kill pathogens.

WHO Guidelines

The WHO guideline for turbidity is less than 5 NTU, which, to the naked eye, looks like clear water.

Turbidity Test Procedure

Turbidity tubes are an easy and cheap way to visually estimate NTU. There are small turbidity tubes available in the World Water Monitoring Day Test kits. You may also be able to order the tubes through your science head or school supply catalogue.

The readings on the turbidity tube will be significantly affected by the amount of light, and the vision of the person doing the test. Some larger particles may settle directly to the bottom, blocking the view. Give the tube a good shake before taking the reading.

pH

pH is a measure of the acidity or alkalinity of the water. The pH for drinking water is generally between 6.5 and 8.0. Water at 25°C with a pH less than 7.0 is considered acidic, while a pH greater than 7.0 is considered basic (alkaline). When a pH level is 7.0, it is considered neutral.

The pH of the water in a stream, river, lake or aquifer will vary depending on a number of conditions: the source of the water; the type of soil, bedrock and vegetation through which it travels; the types of contaminants the water encounters in its path; and even the amount of mixing and aeration due to turbulence in its flow. The effects of a specific type of water pollution on living plants and animals can vary greatly.

There are different methods for testing pH. Litmus paper will give you an indication of whether a sample is acidic or basic. Other tests strips will give you a better indication of the pH value of a sample. pH meters, although more expensive, can be useful in obtaining the precise pH of a sample.

Dissolved Oxygen

Dissolved oxygen measures the presence of oxygen gas molecules in water. These oxygen molecules keep organisms living and chemical process in the water occuring. A high level of dissolved oxygen is generally considered good, while low levels can put stress on fish and organic organisms.

Follow the procedure on the kit that you have for measuring the dissolved oxygen.

Water Quality Testing Student HandoutName ______

Turbidity Test

  1. Be sure you are in a place with good light.
  2. Rinse the turbidity tube with sample water 2 to 3 times.
  3. Place a sheet of white paper on the floor
  4. Hold the tube vertically and pour your water sample into the tube bit by bit.
  5. Look for the cross or circle at the bottom of the tube after each addition of water. Keep on doing this until the black cross or circle at the bottom of the tube just disappears or blurs completely.
  6. Hold the tube vertically and read turbidity in NTU using the graduation on the side of the tube. The result is the value of the line nearest the water level.

Record your results here:

What do your results mean?

pH

Place a test strip in each sample. Record your findings below.

a)

b)

c)

d)

e)

f)

g)

What do these results mean?

Dissolved Oxygen

Follow the instructions on the package for the dissolved oxygen test. Record your answers below.

Results:

What might happen if there was a low level of dissolved oxygen in the water:

1