There's 5 things you can do to get more water into your beardie.
Misting - Get a normal everyday spray bottle, fill it with warm water and mist your dragon down daily. At first he most likely won't like it and try to run away but be persistent. Sometimes we have to be just as stubborn as our dragons are
Baths - Give your dragon a
bath every week (even twice a week if you can) along with misting every day. A dragons skin is made to soak up the water and that will
hydrate him as well.
Dripping water - From the spray bottle or just off of your finger try dripping water onto your dragon's nose. This is how they get water in the wild, they stand under a plant leaf in early morning and let the dew drip onto their noses then lick it off.
Water Bowl - Contrary to belief some dragon's do like
drinking from water bowls. Try putting a shallow dish of water in the tank with your dragon
Lettuce - It has no nutritional value to it but it's packed with water so try mixing in some lettuce with his other greens.