Ok, as you might have read, I tested a Nerf homemade with water in the air chamber. WOW. The output was really good, much of the tank gone in less than half a second. The recoil also threw me backwards and I would have fallen had I not been standing right next to the house. The optimal mix was about 2/3 water, 1/3 compressed air. I can't tell what the output is yet, I will have to attempt to measure and time it somehow. The only problem was that I had to level it, otherwise it would shoot mist. I might make an inverted T gun that could fire angled. That would make a sweet one shot riot blast of unheard of output.

I'm guessing here....did this result in a big shotgun-like, riot blast shot, as opposed to a high range shot?

Both, depending on the air/water mix. Too much water and not enough air or too much air not enough water produced a riot blast. Just the right amount of both produced a very large, potent stream. However, I could only fire level or lower, the range was about 40ft when shooting off the porch at a -10 degree angle.

I have plans to build a new one just for this purpose, one that can be fired at an angle and send a giant stream farther.

You might want to put a nozzle on it... That would increase range. Isn't this just kind of a PC with a long barrel?

It is indeed nothing more than a pc, I took the barrel off. When I make a new one designed for this, it will have a nozzle as well as a larger ball valve. The 3/4" valve probably limited the amount of output it produced.

The new one could turn out to be the ultimate melee weapon! The stream it makes is simply astounding in size and recoil. Could have used a properly designed one today, it would have drenched multiple people in one shot beyond the range of all soakers.

Uhm...isn't a melee weapon a weapon used for bonking the opposing team? But this does sound interesting, I might try it...

EDIT: by "try it" I mean try building one of these guns, not try bonking the other team with them :P

It seems kind of a waste of water for it to fly everywhere. If I were you, I'd put an end cap on it and cut a slot in it (from one end to the other abour 1/4" wide) so that it goes into a more horizontal blast. Then you would be able to soak more people at once and if you wanted, completely DRENCH someone when you turned it sideways.