This drinker has been designed for qail keepers but can effectively be used for any birds.
It can be easily attached to the cage and it connects to water supply source with a 14-16mm (inner diameter) flexible hose. When the water fills up the cup to a certain level it pushes it down and closes the water inlet.
Whenever the birds drink water, a built-in spring lifts up the cup and the inlet opens up automatically letting fresh water into the cup and closing the inlet again. That way constant level of fresh water is always maintained in the drinker cup.
The top screw allows to change the desirable water level in the cup. The bottom protector keeps the birds from pushing up the cup and eliminates the risk of over-spill.