Place the birdbath where you want it in the yard or garden. Slide a shepherd's hook into the ground beside the birdbath. Alternately, clamp the shepherd's hook to the side of the birdbath's basin. If there are tree branches overhead, use them if you prefer.
Paint a milk jug or plastic orange juice bottle with spray paint suitable for plastics. Allow the paint to dry.
Grip a needle or straight pin with a pair of pliers. Hold the sharp end of the needle or pin over a candle's flame until the metal glows. Press the hot point into the bottom of the plastic container to create a small hole. Poke a small hole in the top of the plastic container's lid as well. Do not make the holes very large or the container may empty too quickly and overfill the birdbath.
Create a hanger for the plastic container out of twine, string or thin wire. Wrap the material around the neck of the container to hold it, or weave an open, mesh-like cradle for the bottom of the container. Leave a loop on the top of the container to hang it.
Hold your finger over the hole in the bottom of the container as you fill it with water. Hang the container from the shepherd's hook. Adjust the hook, if necessary, so the water drips into the birdbath.