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Water Quality Control Center

That tropical water really looks inviting! Looks can be deceiving. Before you jump in for a swim, do a little rough science to check if that water's as pure as it looks.

The Challenges!

Test the Acidity of Water

We want to know if the water on your island is acidic or basic (alkaline). Strongly acidic or strongly alkaline water can be a sign of pollution and can be harmful to plants and animals and hazardous to drink. Carry out the following test to check your water.

You'll need:

  • a red cabbage
  • medium-size bowl
  • grater
  • strainer
  • small plastic or glass pitcher
  • 5 clear plastic cups
  • baking soda
  • lemon juice
  • vinegar
  • cola
  • distilled water
  • "island" water (spiked with something acidic like vinegar)
  • teaspoon

What you do:
Grate one cup of red cabbage into a medium-size bowl and cover it with 1/2 cup cold distilled water. Let it sit for 45 minutes. When the water turns red, strain the cabbage juice into a plastic pitcher. Use the cabbage juice to test for acids or bases. Acids will make the cabbage juice turn different shades of red, and bases will make it turn different shades of blue.

Pour an equal amount of cabbage juice into five plastic cups. Add 1 teaspoon of baking soda (which is a base) to four of the cups.. The stronger the acid, the less liquid you'll use to get the original color back. The fifth cup is your control. The color of the juice in the cup with just the baking soda is the color that you want to get all of your mixtures to match.

Add the lemon juice, 1 teaspoon at a time, to your first cup. How much lemon juice did you have to add to get the cabbage juice back to its original reddish color? In the second cup repeat for vinegar, and cola in the third cup. The liquids you need to use the least of are the most acidic. The liquids you need to use the most of are the least acidic. The liquids that don't change the color at all are bases. Now that you have a range of reactions for comparison, test island water in the fourth cup. What is your conclusion? Is it acidic or basic?

What's going on?
Red cabbage juice is an indicator. When it comes into contact with a base, like baking soda, it turns blue/purple. When it's mixed with an acid, like vinegar, it stays red/pink. Pure water is neutral — neither acidic nor basic.

For more information, see Rough Science episode 1: "Mapping it Out"

Test the Hardness of Water

Water can be "hard," even though it's a liquid. Hard water contains lots of minerals (such as magnesium and calcium) that leave deposits in pans and water pipes. Hard water also makes it difficult to lather up with soap. Are you concerned about the lack of lather when you soap up on the island? Test your water to see how hard it is.

You'll need:

  • "island" water
  • two screw-top jars
  • teaspoon
  • eye dropper
  • small open jar
  • tall drinking glass
  • distilled water
  • liquid soap
  • Epsom salts
  • measuring cup

What you do:
In the small jar mix a teaspoon of the liquid soap with cup of the distilled water to make a soap solution. In the tall glass dissolve 1 teaspoon of Epsom salts in 2 cups of distilled water to make hard "island" water. Pour distilled water into one screw-top jar and the same amount of "island" water into the other. Use the dropper to put one drop of soap solution into the jar of island water. Screw the lid on tight and shake. If the water doesn't foam, add another drop of soap solution, screw on the lid, and shake it again. Repeat until the water foams. Count how many drops of soap solution you need. Repeat the experiment using the screw-top jar of distilled water. Which water needed more drops of soap solution to make it foam?

What's going on?
Distilled water is "soft." We can use it as a measure of the hardness-the mineral content-of the "island water." In hard water the salts (magnesium and calcium) interact with soap to form a scum that will not form bubbles (soap foam). Therefore, the amount of lather is related to the hardness of the water.

For more information, see Rough Science episode 10: "Sustenance and Sayonara"

Make a Microscope

Water is full of plants and animals that are too small to see with the naked eye. Make a simple microscope to see if you can detect any tiny organisms swimming around in the water.

You'll need:

  • empty matchbox
  • piece of thin, transparent plastic (e.g., from a plastic bag or plastic wrap)
  • matchstick
  • petroleum jelly or lip balm
  • dropper
  • scissors
  • transparent tape
  • water samples (e.g. from an "island" pond)

What you do:
Cut out most of one of the large sides of the matchbox sleeve. Be careful not to cut it all out since the sleeve still needs to hold together. Next cut a piece of thin, transparent plastic the same size as the end of the sleeve (where the tray slides in). Tape the plastic across the end of the sleeve, taking care to keep the tape right to the edges. Cut a hole in the side of the sleeve to allow light to enter. With the plastic-covered end up, slide the sleeve onto the tray of the matchbox (as if to close the matchbox) with the hole on the open side. Using the matchstick, draw a circle of petroleum jelly on the plastic. Use the dropper to place a single drop of water in the circle. Put another drop of water (pond water) on the end of the tray and look at it through your magnifying water drop. Very carefully, slide the sleeve up or down to focus your microscope. This matchbox setup can also be used to view other items like small insects.

What's going on?
This is a simple type of light microscope that bends light reflected by an object to make a larger magnified image.

Activity adapted from "How to Build a Mini Microscope" at http://physics.about.com.

For more information, see Rough Science episode 2: "Bugs and Barometers"

Build a Water Filter

Worried about the quality of drinking water on the island? Filtering is one of the best methods of making water safe to drink. This filter will remove small particles from dirty water. Make your own filtered water using this method.

You'll need:

  • 2-liter soda bottle with cap
  • serrated knife
  • napkins or paper towels
  • gravel, sand, charcoal, and cotton balls for the filter
  • dirty water (if your "island" water looks too clean, add cooking oil, food coloring, pieces of paper, or tiny pieces of Styrofoam)
Water Filter

What you do
Remove the plastic sheath from the outside of the soda bottle and screw on the cap. Cut the bottle in half. Put the top half of the bottle upside-down (like a funnel) into the bottom half. Line the upside-down half-bottle with a napkin or paper towel. Put layers of gravel, sand, charcoal, and cotton balls inside the top half of the bottle. (Ask participants to predict what they think each of the filter materials will remove from the water.) Remove the bottle cap. Pour the dirty water through the filter. (Ask participants to comment on any changes they notice and how their observations fit with their predictions.) Now scoop out each layer of the filter and examine what each layer has taken out of the water. Experiment by putting the filter materials into the bottle in a different order each time. What difference does the order of the layers make? Clean the bottle halfs thoroughly before you use them again.

What's going on?
Different materials filter different substances from the water. The slower the water travels through a material, the more impurities are removed. Here the cotton fibers and sand create a longer path for the water and impurities to pass through and solids get trapped. Charcoal particles are charged (like a glass rod rubbed with a silk cloth) and they attract oppositely charged impurities.

For more information, see Rough Science episode 2: "Bugs and Barometers"

Make a Water Clock

The island sundial relies on the sun. So how will we know the time after dark or on a cloudy or rainy day? This water clock, based on an ancient Chinese design, will keep you on schedule. It marks time every 5 minutes. Use it to keep your water treatment activities on schedule.

You'll need:

  • sundial or kitchen timer or alarm watch
  • 5 paper cups (all one size)
  • clear glass jar at least as big as the cups
  • 5 thumbtacks
  • transparent tape
  • pencil
  • strip of heavy cardboard
  • strip of paper
  • water
Water Clock

What you do:
Prick a hole in the bottom of each cup with a thumbtack. Pin the 5 cups to the cardboard with the thumbtacks, one cup above the other. Tape the strip of paper vertically on the glass jar; place the jar beneath the bottom cup. (Test the apparatus: fill the top cup with water and make sure the water drips smoothly through each cup down to the glass jar, then empty the water from the cups and jar.) Fill the top cup. Using your sundial or other timepiece, every 5 minutes mark the water level in the glass jar on the strip of paper. When the glass jar is full, you will know how much water represents a five-minute interval. Now you can use the water clock to keep track of time.

What's going on?
The water clock measures time against a known scale of five-minute intervals. This not unlike a sand timer that has been calibrated to take a period of time to move from the top to the bottom.

For information on making other types of water clocks, see http://nationalgeographic.com/world/trythis/try10.html.

For more information, see Rough Science episode 3: "Time and Transmitters"