This inquiry was part of our unit on water. To introduce the science concepts and skills in testing water for hardness, pH, copper and chlorine, students participated in four guided activities that explored the quality of water. Each day, we completed one test on the water in our classroom using Hach Water Quality Test Strips. Students had a one- to two-page overview of each test and directions to follow using the test strips. After each test, we recorded the results and discussed what the data meant. For example, because most water pipes are made of copper, you would not want a pH to be acidic (below a pH of 7) since copper would dissolve from the pipes and go into the water. Pipes that dissolve would also begin to leak over time.

Each activity explained a little about one characteristic of water and guided students in how to conduct the tests. As the students worked, they built their understanding of the nature of water as a solvent and improved their ability to apply some of the skills of scientific investigation. Students were then encouraged to compare different water samples in order to answer the question: What makes water good?

This task provides information to the teacher about whether students are building an understanding of the characteristics of water and can use scientific reasoning to evaluate the quality of water for particular uses (for example, if water is hard, soap does not work well; however, it is not bad for drinking).

This task demonstrates how well students can use scientific tools to collect data and show evidence of conceptual understanding in how they interpret data. Students have the opportunity to communicate their results to the class and learn from what other students have investigated.

After the guided investigations with the whole class, teams of two to four students then repeated the tests with the classroom water and chose a second water sample from several choices of bottled water to conduct the four tests on. Finally, students interpreted their data and discussed conclusions based on the data collected. Each group shared their investigation and results with the class. Class sharing is a way that teachers can check understanding, make connections to prior knowledge, and extend thinking to the next lessons in the unit and/or introduce new science vocabulary.

Note: For teachers who have little background in conducting these tests, the Hach Water Quality Test Strips and teaching materials are user-friendly and written for easy conceptual understanding, even for third graders.

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Students may want to conduct further investigations with other water samples, such as the water they have at home. Concepts learned in these activities can build a foundation for more in-depth investigations with solvents and solutions.

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Understandings about the Nature of Science (see appendix)

Guiding questions to ask students before, during and after investigations might include:

• What makes water hard or soft? What does that mean? How does water become hard? (Water, a solvent, picks up impurities easily. When water flows over rocks, it can pick up calcium and/or magnesium salts from limestone or other rocks. These salts dissolve in the water, making it hard.)
• Why doesn’t soap work well in hard water? (Soaps contain long chain-like molecules that have two distinct ends. One end interacts with water and the other end interacts with oil and grease. If there is too much magnesium or calcium in the water, the end of the soap molecule that is supposed to react with the dirt and oil ends up reacting instead with the magnesium or calcium. This makes soap scum – bunched-up soap molecules.)
• How can hard water hurt pipes? (It can accumulate and clog the pipes.)
• What is pH? What does it mean to be neutral? acidic? alkaline? (pH is a way to measure how acidic or alkaline a solution is. The pH scale goes from 0 to 14. If there is an equal number of hydroxide and hydroxyl ions, the solution is neutral and has a pH of 7. Because a water molecule is made of one of each ion, pure water is neutral. If the solution is less than 7, it is acidic; greater than 7, it is a base, or alkaline.)
• Why do some water suppliers (like the town) add alkaline substances to the water to raise the pH? (To slow or prevent acidic water from “eating” the pipes from the inside.)
• Why are there sometimes blue-green stains in your bathtub? (Copper has dissolved in the water.)
• What do your results tell you? What did you learn from your results?
• What conclusions can you make based on your results?
• What new questions do you have about water?
• Have you learned anything that surprised you?

(Unifying concepts/big ideas and science concepts to be assessed using the Science Exemplars Rubric under the criterion: Science Concepts and Related Content)

Physical Science – Properties of Matter: Students observe and compare physical properties of matter to make predictions and classify materials.

Scientific Method: Students observe and explain reactions with some justification, using data and prior knowledge, when variables are controlled (cause and effect). Students determine the patterns and/or which kinds of change are happening by making observations and measurements over time (change and constancy).

Earth and Space Science – Earth Structure and System: Students observe that water is a solvent. As it passes through the water cycle, it dissolves minerals.

Science in Personal and Societal Perspectives – Personal Health: Students understand that nutritional balance has a direct effect on growth, development and personal well-being, and that the water you drink and cook your food with can affect your health.

Mathematics: Students collect, organize and analyze data appropriately and compare attributes or effects.