How Do I Wean Him Totally?

I had been looking after 2 baby budgies after Mum left the aviary door open and all the females excaped. The runt died on Thursday and I am left with a very attention demanding budgie. He still wants his hand rearing food even though he seems to be eating seed/ grasses. How do I wean him completely off the hand rearing food and how do I know he is getting enough water? I have seen him stick his beak into the dish, but he is not drinking only shaking his head. I have only been giving him a small amount of hand rearing food in the morning and the only reason I am still doing it is so he doesn't dehydrate. Can someone please help me???