Budgies drink very little if they have a proper diet. The bird may also not be used to the drinking receptacle provided (font?) A small ramekin with water on the bottom of the cage will soon make it drink if it is thirsty.
In the wild, budgies may sometimes go without water for 4 or 5 days without harm. They get a lot of the required moisture from the seeds and stuff they eat. The droppings also contain an absolute minimum of moisture so not much is lost.