Ha, it's not really a double post if I give the same answer in two different active threads, is it?
To wit:
Try using a 1 gallon plastic waterer, up on a
tall block(s) atop a plywood platform as mentioned in another recent thread in order to prevent litter and poo getting kicked into it, and put it in a CORNER where it cannot be knocked over, and do some sort of anti-roost measure atop it (a variety of easy options exist).
With four chickens I'd suggest that's your best option.
For completeness though I will show you my compact very small homemade waterer I was using in my tractor last summer, not as the main waterer (that was outdoors) but just so my 2 ISA Browns did not get too thirsty if I let them out a bit late:
It's vacuum-style; to refill it, I dismount the whole unit from the wall (attached by bayonet-style mount involving screw, and rests on a block for further support), take it out of the tractor, turn it upside down (yeah, some water spills out) then dump and refill the bottle, reinsert into rubber band, and turn back upside down again and replace into tractor.
This is really too small for 4 chickens though (in principle it could be sized up, but I can't think offhand of what materials you'd use so scrounging just the right things could be a real problem). Seriously, I cannot see why a properly-raised non-roost-on-able 1 gal waterer in the corner should not be quite satisfactory.
Good luck,
Pat