Hydration

Yes, Bearded Dragons Need Water
You need to spray/drip hatchling and juvenile dragons with water 1-2 times a day and sub-adults to adults once. Only mist your dragon during the day and your heat-basking lamp is on. When I say "misting" or "spraying" I mean one light spray with a spray bottle do not soak the entire cage. Over watering in combination with a dirty cage can lead to respiratory infections, so keep it light.
Water Bowl Tricks
You can try putting a small water bowl in their enclosure but to get them to drink from it is tricky. You can guide them to the bowl by spraying them and leading them to it. You can also try adding a little bit of flavor. We recommend something organic, all natural fruit juice like apple or pear, just enough to flavor the water and make it appealing and choose something that is 100% juice with no sugar. Continue to do this until you see your dragon start to drink, the sweet smell should attract them, then replace it with regular water from then on. Once they have realized they can satisfy their thirst with that bowl they should keep coming back. Make sure you clean the bowl well as many dragons will defecate in standing water. Some dragons are stubborn however and will only drink when sprayed when they are given water from a dropper or only drink when in the bath.
Some bearded dragons need to be lead to water to know it is there, simply lightly mist them and then show them the water dish.
Some bearded dragons will be drawn to water right when you pour it in their bowls, the sight of the flowing water attracts them by natural instinct, though most do not like being watched.
Some bearded dragons will only drink when sprayed, if you have to excessively spray to get your dragon to drink, do it outside your cage to prevent the growth of bacteria.

 Dehydration

Dragons need water just like we do. Proper hydration is very important in the health of a dragon and is even more important to a sick dragon.  Dehydration can cause kidney failure and death, if your dragon appears dehydrated offer water asap. If they are lethargic, unable to hold their head up, or are not moving or eating, contact a Veterinarian right away.
This image is of a severely dehydrated bearded dragon from Flickr