Ok, the second cheapest bottle of water at Dublin Airport is upstairs in the cafe after you go thru security. If you are buying food, you can get a bottle of water for 1.30.
The cheapest bottle of water is in the business lounge, it's free! As long as you have a card that lets you use the business lounge, you can have all the water you want; in fact I usually throw a couple of bottles in my briefcase for later.
No sign of a water fountain (or even a water foundation) in area B, I walked around it twice and couldn't see anything.
Oh and my apologies, fell down on the job as AAM researcher, I forgot to bring an empty water bottle with me throughsecurity to see if they would confiscate it. Willl do it after christmas!