avbrand.com writes: [via]
I decided it was time to build an automatic water dish that refills itself. I bought an icemaker water hookup (designed to attach the icemaker in a fridge to the water supply) and my friend Frysteev helped me plumb it in. The tiny 1/4-inch water line runs to the top of my kitchen cabinets, where it enters an irrigation valve ($22). This valve then runs to some clear tubing, down from the cabinets and into the water dish. Also in the water dish are two sensor wires, one at the bottom and one at the top of the dish.
Automatic Pet Water Dish Filler – [Link]