How to Build a water clock?

November 26, 2021
Water Clock

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.