I was also very annoyed having to fill the waterer up everyday, thanks to the chickens running around and knocking into it.
The one I made works by the same principle as the store bought ones, by maintaining a vacuum.
Step 1: Parts!
4 2" elbows
2 2" T's (one 2"x2"x 1/2", one all 2")
2 Ball valves
2" PVC pipe
1/2" PVC pipe
1 1/2" cap
1 4" cap
1 Uniseal (http://www.aussieglobe.com/index.htm)
Step 2: Cut pipe and dry fit everything!
Take care to ensure that all the pipes cut are clean and all (slag, pvc shavings, burrs, dingle berries) are removed.
I used 2 ft length pipes and found out that it had a 1.5 gallon capacity.
If you want to increase the capacity you could make the pipe longer or add cross members.
Step 3: The water bowl.
Also, on the down pipe you need to drill a set of holes, these holes need to be below the lip of the cap.
As the water fills the bowl, the holes allow air into the system thus allowing more water out. When the water covers the hole, air can't enter the system and the water stops flowing.
Step 4: Glue everything together.
I put two valves on the system, one open and one closed.
When filling it up I close the bottom one and open the top, and when in use it's reversed.
Make sure to let the glue set before using the system.
Step 5: Put it to use.
This new system only has .5 gal more capacity, but lasts 3-4 days between filling.
Since the chickens can"t budge the water bowl, they can't spill the water.