Very few bearded dragons will drink from their water dish, they''ll sit in to cool off, they'll do their poos in it (doesn't take the long to discovered a submerged poo isn't as stinky).
In the wild in their natural range a bearded dragon can live out it's entire life without ever experiencing rain or flowing or standing water (except at permanent springs natural or man-made), and they get the moisture they need from the small animals , and insects the catch and eat, and from herbs and flowers and from fruit they find.
I don't have water dishes in my beardie's tanks. I'll mist the beardies in hot weather, and drip water on their snouts , and other than that my beardies get all the hydration they require from their daily live insects and greens.
CBDs: Puff ( RIP 10Dec2015 (3.2 years old (aneurism)) ,Rex (RIP 16Mar2017 at 4.6 yrs old (unexplained death)) , both adopted at 6wks old..Toothless & Peppa : (5 wks old 19dec2015).
Eastern BT Skinks : George & Mildred (born Sept 2010).
Eastern Water Skinks : Lucky (wild juvenile), rescued from a cat.Taken by a SI and far too soon, 9mths with us. RIP 21Jul2010.Wriggles - (rescued injured), small lizard thought she was a big lizard, 7-8 yrs old, died in her sleep, RIP 2Feb2016.)