Here’s a fun STEM project for kids that is perfect for warm weather – build a LEGO® water wheel and experiment with fluid dynamics.

Build a Water Wheel: Engineering with LEGO and Water

It was actually not shockingly hot over the July 4th weekend (we live in Texas), and we enjoyed playing outside with LEGO®!

First, Aidan used duct tape to secure some base plates to our oil change tray.  We bought this a few years ago in the automotive section at Walmart – it’s quite useful for playing with magnets among other things.

Lego Water Wheel

Then we started building!

Lego Water Wheel

We used a propeller brick to build a water wheel.  We originally had the water wheel on the top of a tower of bricks, and it turned quite well when we poured water over it.  But it was much more impressive with the hose aimed directly on it!

The water wheel will only turn in one direction, and it’s fun to have kids work out how to build it and which way the water should flow.

LEGO Water Wheel

Want to see it in action?

Then we created a door that can open or close to either hold back water or let it flow.  (The door stays open from the force of the water unless you physically close it.)

Engineering for Kids: Build a LEGO Water Wheel

The door pivots on two axle bricks.

Engineering for Kids: Build a LEGO Water Wheel

Aidan built barriers for the water to flow around:

Engineering for Kids: Build a LEGO Water Wheel

And Owen wanted a pool for his crocodile at the bottom.  We leaned the oil change tray on the edge of our patio to give it a little bit of a slope.  The only problem was that the boys would lean on the tray which bent it… It did bend back but I wished we had something more solid to use for our work surface.  If you have a board or something, use that instead!

Engineering for Kids: LEGO and Water

LEGO® bricks and water – what a great way to cool off on a summer day!

LEGO® is a trademark of the LEGO® group of companies which does not sponsor. authorize, or endorse this site.

Engineering for Kids: Build a LEGO Water Wall


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  1. Michelle Jul 7, 2015

    How have I never thought to combine Legos and water? That is so inspired! I love the oil change tray too. I also never would have thought of that, but it's such a good idea for so many different activities.

    1. Fiona Dec 31, 2017

      How does the water not leak through the Legos?

    2. The Reading Residence Jul 8, 2015

      What a brilliant idea! One for the summer holidays, thanks for sharing

      1. Christine Jul 8, 2015

        Have you tried floating objects down the maze? Maybe a little boat or ping pong ball. Thanks for sharing this fun idea.

        1. Jenni Jul 9, 2015

          Can you post some instructions for the door and the wheel (or is that part of my challenge? ) Brilliant idea! X

          1. Juliet Jul 11, 2015

            Give it to your kids! My 7 year old managed to build the wheel and door by just looking at the pics.

            Great idea, my kids both had fun with it (5 & 7yo)

          2. Stef Aug 8, 2015

            A great project! I should look for an oil change tray as it looks like a good starter for many projects. Thanks for sharing

            1. Erin @Nourishing My Scholar Aug 15, 2015

              This is totally awesome!

              1. P.S. Jan 29, 2016

                This is amazing. I was looking for a way to make a waterwheel and demonstrate some engineering principles to my two little girls, when I came across this site. We quickly constructed a water wheel using Lego parts scavenged from a 'Girls of Heart Lake City' set. The water-wheel is powered by the kitchen faucet and drives an elevator spool to lift up figurines. Works very nicely. My girls loved it. Thanks for the inspiration.

                P.S. I would attach a picture of our project if this blog supported that feature.

                1. Josie Lynn AWESOME Sep 29, 2017

                  AWESOME project!!! Super fun anytime!?!

                  1. cammy Apr 15, 2020

                    that is cool


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