DOGGYWORLD.com

"The WaterDog automatic outdoor pet drinking fountain lets your dog help itself to fresh water, so you don't have to worry about stagnant or empty water bowls. WaterDog senses your dog's approach, and automatically dispenses a cool, clean stream of fresh drinking water. Smart sonar sensing technology triggers the WaterDog to turn the water on when your pet comes within three feet (one meter), and turns it off when your pet leaves. You'll never have to worry about what your dog's been drinking again!
The WaterDog:
operates automatically, providing fresh water when your pet approaches
accommodates your dog day and night for up to one year on four C-cell batteries
connects quickly and easily to any outdoor faucet
includes a flow-through connector to accommodate your garden hose as well"