A laser shined through a clear, water-filled container will follow the water stream downward.

This is a recreation of a classic demonstration from the late 19th century, attributed to Jean-Daniel Colladon. Aim a laser through the hole in a container filled with water. If you aim the laser carefully (and you have a dark room) you can see that the laser is internally reflected in the outpouring water stream.

This demo will work well, but you need time to set it up carefully, and a big enough bucket (and good aim) to catch the water, or you'll make a huge mess.

LDL-B3. The container and instructions are stored in a cardboard box. You'll need a laser and something to catch the water.