Water Pressure Rockets were a terrific toy. I remember purchasing them for under a dollar in the 70s. They were small plastic rockets, usually red and white in color. You put a small amount of water in the rocket and then attached an air pump.
Once you had pumped in enough air pressure, you could release the rocket and it would zoom straight up in the air, leaving a trail of water and mist.
It was a good thing they were cheap because most of mine got stuck on the roof or in the top of a tree. Being an inventive kid, I tied a bunch of bottle rockets around one of these with a string and set it off. Yes it worked!