What do eastern water dragons eat?

First off, it's Drink, not eat. They would probably drink a lot of water, depending on their size. One story tell about how a dragon ate a sheep stuffed with sulphur, and got so thirsty it drank half a river and exploded.

Actually they do eat like every other normal animal. Water dragons are Omnivors, so they eat Mealworms, crickets and other veggies but they will refuse to eat veggies but its good to make them eat veggies once in a while though they do prefer moving animals/insects. Water dragons are like Bearded dragons but you feed a water dragon until it refuses to eat anymore so keep a schedule so they can get used to their normal feeding.