Hi fellas,

This may be an unusual question on this forum, but I thought I'd try posting it here. I hope I'm not violating your policies by doing so.

I'm builing a water cannon for casual fun at the lake. I have a pipe with a diameter of 18 mm (≈4/5") that will serve as the "gun" which will project the water. The idea would be to use an electrical pump to suck water directly from the lake, which would be powered by a car battery or something similar.
Now, I want this guy to be able to shoot a beam of a good 4 meters, or 12 feet.
Let's say the hoses used from the water to the pump, then pump to gun, would be about 18 mm, what kind of power and output (gallons/h) will I be needing on the pump?

I know nothing about this stuff, so layman's terms are appreciated. Also, if you have any tips to share on what is important to consider when doing this kind of project, I accept with open arms.