Water Bottle Boats: Discovery at Home

Materials Needed:

  • Two empty plastic bottles
  • Paper
  • Markers
  • Crayons
  • Tape 
  • Scissors
  • Bathtub for testing or bucket with water
  • optional : crayons, lids, glue, popsicle sticks 


  • Attach two water bottles together with some tape.
  • Add a sail to your boat by using a pencil or popsicle stick in the middle of the two water bottles. 
  • Add the flag by cutting a triangle out of a piece of paper and attach it to the top of your pencil.  
  • Decorate your boat! You can use markers and crayons to add designs. Cut paper and tape/glue it to the boat.
  • Once decorated, test your boat in water to see if it floats or sinks. Add more or less to your boat to see if this makes a difference. 
  • While your boat is floating, try adding an object on your boat to see if it can hold it. How many toys can it hold before sinking?

How to Expand it:

  • Put other objects in the water. What floats? What sinks? What’s the difference?
  • Move your boat from one side of your tub to the other without touching it.
  • Redesign your boat and test out different designs. Will one water bottle work? What other objects can you use to build a boat


What do kids learn?

  • Density is what decides whether an object sinks or floats in water. If something is less dense than water, it floats. If something is more dense than water, it sinks.
  • Using plastic bottles to make toys is a great way to encourage imagination and reuse of single-use products.
  • Science Vocabulary:
    • Density - The weight and size of an object. A fluffy pillow has less density than a brick. A crayon has more density than a feather.
    • Sail - a piece of material extended on a mast to catch the wind and propel a boat. Real sailboats rely on the power of wind to travel.