Water safe to drink

Year level: Middle primary/ Upper primary Learning outcome Students will compare two methods of making water safe to drink: using alum and boiling; and boiling and distilling. Note: The activity, Cleaning dirty water is a prequel to this activity, though not essential. Read Water: Good servant, bad master Examine photos 1 and 2 in the case study. Annotate them with comments about the collection and use of water. Activity 1: Alum and boiling (the method used by Quach Thoi Dae) Preparation One cup of muddy water Two clean glass jars ½ teaspoon of alum (aluminium sulphate, available from stock feed agents, hardware stores and some chemists) Stirrer or spoon Saucepan Stove or electric hotplate Clean piece of plastic wrap Black marker pen Method 1. Stir the cup of muddy water and pour it into one of the glass jars. 2. Add the ½ teaspoon of alum and stir. What happens? 3. Leave the mixture of alum and muddy water for a few minutes. What has happened? 4. Carefully pour the ‘clean’ water from the top of the mixture into the saucepan. Bring it to a boil and let it boil for three minutes. Turn off the heat and let the water cool. 5. Pour a ¼ cup of the boiled water into the second clean jar and cover it with plastic wrap. 6. Label the jar with your name and ‘Activity 1’. Activity 2: Boiling and distilling Distillation requires boiling water, collecting the steam (or water vapour) and turning the steam back into liquid water again. Preparation One cup of muddy water Small, clean saucepan and lid Stirrer or spoon Stove, or electric hot plate Clean glass jar Wet cloth or kitchen sponge Clean piece of plastic wrap Black marker pen Method 1. Stir the cup of muddy water and pour it into the saucepan. 2. Place the lid on the saucepan so that it is on an angle and overhangs the pan. 3. Place the jar so that it can collect the runoff water. Also place the wet cloth on top of the lid. (See diagram). 4. Bring the muddy water to a boil. Take care not to touch the saucepan or the lid while it is boiling. 5. Once ¼ cup of water has collected in the jar, turn off the heat. Cover the jar with plastic wrap and label it with your name and ‘Activity 2’. Comparing the results Observe the water in the jars. Fill in the first row of the results table. Then leave the jars of water on a window sill for a week. Observe the water again and fill in the second row. Making water safe to drink results   Activity 1: alum and boiling Activity 2: boiling and distilling When the water was put into the jars What does the water in the jars look like?     One week later What does the water in the jars look like now?     Questions to answer 1. Which activity required the use of a chemical? 2. Which activity used the most energy (heat)? 3. If you were living in a place with no electricity, but plenty of wood, which method would you use to purify your drinking water? 4. If no cheap fuel or wood was available (and presuming you could obtain alum), which method would you use to purify your water? 5. Consider your results at the end of a week. Which method do you think is better to purify water? Why do you think so? (The distillation process removes almost all impurities from water.) 6. Create a PMI table comparing the two methods of purifying water. Assessment task Write a report comparing the two methods (alum and boiling; and boiling and distilling) that can be used to purify water, assessing the pluses and minuses of both methods. Extension Do an internet search to find a solar distillation method. Discuss the pluses and minuses of using a solar distillation unit.