I don't know if it's the best way, but I use a childs medicine syringe ( or dropper ) to offer water. I find that it's the best way for me to know my dragons are drinking.
I do this by putting a drop of water on the tip of their mouth and wait for them to start drinking. As they start drinking I put more drops on the tip of their mouth. I do this until they are done. Don't worry, you're dragon will let you know when it's done.
My dragons don't drink everytime I do this, which is at least once a day for older dragons and twice a day for hatchlings. Your dragon will let you know when it doesn't want any water by not drinking, turning it's head away or even shaking the water off.
Crickets also contain a lot of moisture in them. Just like us, they are mostly water. Don't be surprised if your bearded dragon eats a ton of crickets, but doesn't drink any water.
As for leaving for a day. Your dragon should be fine with a nice bowl of greens, vegetables, maybe some commercial bearded dragon food, and a bowl of water. If I leave for longer than a day, I have someone check up on my dragons ( usually my father ) and give them fresh food and water. I think this is even more important for young dragons that are growing rapidly.
I hope this helps answer your question.
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Eric Nelson
http://www.beardeddragonresource.com/