This science experiment is a splashy hit, as long as it works correctly! You’ll teach kids something about air pressure, plus create a fun way to get wet on a hot day.

First, we needed to blow up a balloon inside a bottle…but there’s a catch. Insert the balloon into an empty bottle, folding the edge of the balloon over the bottle’s rim. Huff and puff with all your might and it won’t blow up, because there’s nowhere for the air pressure to go!

Next, we cut a small slit in the bottom of the bottle. Now, when I huffed into the balloon, it could inflate! It’s fun to watch this inside the bottle, almost like a lung filling up.

The next part is a bit tricky. Keep your finger over the slit in the bottle, and ideally your balloon will stay inflated because now the pressure can’t escape. With your finger still cover the hole, fill the balloon with water.

When you release your finger, the water explodes!

It was tricky to do this solo, though, and eventually we ended up filling the balloon with water before inflating it. Then, we got a mini squirt of water when I released my finger from the slit. You can see our rather unimpressive puddle here:

Are you able to get a huge water volcano? Please share in the comments!