American Chemical Society. Adapted with permission.
People interact with Earth’s water (hydrosphere) in a variety of ways. We depend upon water for survival, but we also need it to keep clean and help avoid spreading disease. On our ever-changing Earth, the supply of fresh water can be limited for some humans. We need good techniques to make the best use of the fresh water we do have.
For example, when you wash your hands, how do you do it? With soap and water? With water alone? Do you scrub your hands or simply rinse them under the faucet? Does it even matter? Yes, it does!
For each group of four students:
- Nonstick cooking spray
- Ultra-fine glitter
- Timer or watch with a second hand
- Access to a sink with warm and cold water, soap, and paper towels
- Data sheet (a sheet of paper with 8 small outlines of hands drawn on it)
- In your group of four students, make sure that you each “dirty” your hands. First, coat your hands lightly with nonstick cooking spray. Spray over a sink or newspaper, because the floor will get very slippery if the spray gets on the floor. Rub hands together to thoroughly coat the front and back of your hands and between all fingers.
- Continue to “dirty” your hands by sprinkling one hand with glitter and rubbing your hands together. Cover the front, back, and fingers of both hands. The glitter represents bacteria typically found on your hands.
- Wash hands as follows:
- Student 1: Wash with warm water, rinsing only (no scrubbing or soap) for 5 seconds.
- Student 2: Wash with warm water, scrubbing for 20 seconds under the faucet without using soap.
- Student 3: Wash with warm water and soap, scrubbing hands (while not under the faucet) for 5 seconds, and rinsing just until no soap is left on your hands.
- Student 4: Wash with warm water and soap, scrubbing hands (while not under the faucet) for 20 seconds, and rinsing just until no soap is left on your hands.
- Observe the cleanliness of each student’s hands. Record observations on the data sheet by shading in the outline of a hand to indicate where you still see glitter.
- Wipe your hands thoroughly with a paper towel, and make sure each student in your group does the same. Again, observe and record the cleanliness of each student’s hands.
- Once you’ve recorded all observations, make sure all students completely wash up with soap and water to remove all glitter and cooking spray.
- Discuss: Which student used the hand washing technique that you normally use or that you think most people normally use? Which hand washing method was the most effective? Which was the least effective? What factor do you think is most important in hand washing?
The ultra-fine glitter serves as a visual reminder of the bacteria found on our hands, although the glitter is much bigger than bacteria actually are. Some bacteria can be harmful because they can cause disease or infection, but other types of bacteria found on our hands are harmless to us.
Unfortunately, some people rarely wash their hands. Of those who do, most overestimate how thoroughly they do it. Proper hand washing tips are provided by the Centers for Disease Control and Prevention (www.cdc.gov/Features/HandWashing).
This activity was adapted with permission from “Wash This Way,” Terrific Science, Miami University, Ohio, www.terrificscience.org/healthrich.