can do this by hanging a pail with a slow drip over the water. if you want a better appearance, and are willing to spend more, you can purchase a pump and set up a small waterfall.
second, most commercial bird baths are too deep for most birds to bathe in. you should not fill the bath with more than 2 inches of water. a gradual slope to the deepest part of the bath also helps.
third, it is very important to keep the water clean. if you notice a lot of algae growth, drain the container and wash with a solution of one tablespoon of bleach to one half-gallon of water. 