Looking to build a spitter

brad - did wtwtw say "s p l i t t e r" or "s p i t t e r"?

I read it as spitter (as in, one who expectorates).

In which case, yes, I agree compressed air is probably going to be the easiest solution.
Siphon feed style would work well, I think, for a constant-on set up.
Maybe use a piece of copper tubing - crimp the end, have it blow over the end of a long tube, the other end of which is in a bucket of water - the moving air over the tube creates low pressure, so the water climbs the tube and is sprayed out in the air stream.
Problem being, the amount of air being used - a pretty big reservoir tank would be needed, or an air compressor working full time.

Other choice could be hacking a motorized squirt gun, perhaps?
Here's a nominee: Speed Shark Motorized Water Gun with 32-oz. Tank : Target
Don't know how long the batteries would last - but I can see where that water tank could easily be replaced with a larger water reservoir.
Also, this could probably be rigged to be remotely activated.
But, that takes this out of the realm of "simple".

The spitter I showed you shoots spurts. So it is kind of like being shot with a water pistol. It doesn't soak you, because you can get out of the way. But if you set it up right , it will surprise the heck out of people. It can also be set off by one of those cheap mats, because it is low voltage. A old cell phone charger will run them. The only bad thing about it is the water bottle has to be close. I added a small piece of hose to mine where it draws from. But if you go to far it takes to long for it to get to the tip. A 16 oz bottle will squirt about 50 people. So with the mat switch and a hot line walwart. It should run about less then 15 bucks. Thw wiper motor is a better system. You can even run line to other props, like snakes and frogs, and have water shooting bat people from 6 or different directions. But it will cost you more money. I would guess 30 to 50 bucks, depending on your switch and how many lines you run. Also if it is cold it ain't going to be fun for you. So remember people know where you live!