Why Does Fresh Water Float? In our Updates, Biologist Cathy Beck has mentioned that fresh water will float on salt water. But why? With these simple experiments, you can explore how and why this happens, and what it means for the buoyancy of things in salt and fresh water: Materials Needed 3 Tall clear glasses that can hold at least 8oz. of liquid Fresh (tap) water Salt Food Coloring Eye Dropper Spoon or stir stick Two eggs Activity 1. In a tall clear glass with 8oz. of fresh (tap) water, mix in 7 tsp. of salt and stir so it is dissolved. Then, in a separate small container, mix a few drops of food coloring in a few ounces of fresh water, and stir until well mixed. Now, take an eye dropper full of the colored fresh water, and gently drop it on top of the salt water in the glass. Watch how the colored fresh water floats on top of the salt water. Why do you think this happens? For a clue, try this next experiment. 2. Sink or Swim? What do you think will happen when one egg is placed in salt water and another in fresh water? Before performing this experiment--make a prediction. What will happen to an egg placed in saltwater? In freshwater? Why? Using two tall clear glasses, fill one glass with 8oz. of fresh (tap) water, and mix in 7 tsp. of salt and stir so it is dissolved; fill the second glass with 8 ounces of fresh water. Carefully place one egg in the glass with salt water, and a second egg in the glass with fresh water. Do the eggs float or sink? Why? From what you see, what can you tell about the difference between salt and fresh water? Ask yourself if you seem to float more easily when you swim in the ocean or in a lake? Copyright 2002 Journey North. All Rights Reserved. Please send all questions, comments, and suggestions to our feedback form