Engineering design challenge: Water sample

Engineers work to protect the public, and that includes testing their water to make sure it’s safe to swim and play in. Civil & environmental engineers help to complete water testing to look for harmful chemicals and bacteria. They need devices that will hold the sensors for measuring the water at different depths. Some samples need to be taken at the bottom of the riverbed or on the ocean floor; others need to be taken at the surface of the water. There are still others that need to be halfway down, suspended in the water. Engineers need to think about weight and buoyancy of the sensor and its holder, and how to protect it from the elements.


Create a water bottle sensor-holder that will be suspended in the water, neither floating to the top nor sinking to the bottom.


Instruct participants to use objects they can find around the house to build their project (some examples are below).

We recommend using a spoon as the sensor that the water bottle holds in the middle of the water. Figure out a way to attach it to the water bottle that will be reliable even while the sensor is underwater. Think about how to balance out objects that are heavy and sink with objects that are light and float.

Example materials

Instruct participants to use these or anything else they find around their house to work with:

  • Plastic water bottle
  • Metal spoon
  • A basin to test in – a sink, a bathtub, a plastic storage tote or even a large bucket
  • Elastics
  • Tape
  • String
  • Twist ties
  • Nuts, bolts or washers
  • Paperclips
  • Ping pong balls
  • Fishing bobbers