I was afraid of that. Is there a way to maximize the effects of flow? Do it on a ramp and/or keep the water level around 5-6 to prevent teleporting?
In my experience, the easiest and best way to produce a limited flow of water for a pusher trap is using a diagonal pressure reducer, and you don't even need any fancy mechanics to maintain the water level. The only moving part (aside from the water itself) is the on/off switch floodgates. Pressure (water teleporting) only goes the six orthogonal directions (N, S, E, W, Up, Down). Water will go through a diagonal path, but not by teleporting, just by moving individual units of water between adjacent tiles.
That means that if you provide a diagonal grating on an infinite water source, you get dependable limited flow, which as I recall is enough to provide pushing across a 3 wide path, like so:
It's been a while since I made one of those (too simple and effective, I've been trying to limit myself to either more elaborate traps or military), but that should work as drawn. The fortifications could be done without, but then building destroyers could access the doors, although that shouldn't happen when water is flowing. You could leave it turned off except in case of invasions, or use traffic designations to keep your dwarves out of it and leave it always on (though the constant flowing water will affect fps).
I drew it underground, but there's no reason why it couldn't be placed on a cliff, or the ramparts of your castle, or whatever (other than it being easier to get infinite water underground).
This style of pressure reducer is also useful for managing water levels in other situations, like if you have a cistern well below the water source, you could just have a pressure reducer at the end of the plumbing feeding the cistern, and then it will never fill above that Z level, no matter the pressure on the input plumbing. No more massive floods coming out of your wells, drowning the meeting hall!
You can also put checkerboard columns across hallways or in your entrance hall (I like to put it around the depot, separating 'inside' from 'outside', with the depot being 'outside' but still underground. Not only does that limit line of sight on invading marksmen, allowing your dwarves to ambush them behind the columns, but it also keeps water from flowing quickly through, so that in case of a major flood, you get muddy floor but water is not capable of quickly filling your fortress, so you can lock down the affected area while not limiting your dwarves movements.
Basically, I love diagonal gratings made of checkerboard columns. They are functional, while providing easily visible symbolic boundaries between parts of the fortress, while also being totally dwarf permeable, and if you want to trap the boundary, it halves the required number of traps while also stopping arrow fire, reducing scared dwarf cancelations, and preventing disastrous flooding.