If you want to build a two-stage water rocket, Air Command Rockets has detailed build series over on YouTube[1], from simple soda bottle setups to a custom rocket that they got[2] to over 1600m (5000 ft).

That's air and water propelling a rocket a mile up!

[1]: https://www.youtube.com/@AirCommandRockets

[2]: https://www.youtube.com/watch?v=GCaiK3Zqs4M