1) when you "expel" water it feels like you should put a water stone in the center afterwards, to go with the description. It also makes the water breath slightly riskier: seems quite easy to do a lot of damage with it otherwise. But this isn't in the rules, so it doesn't happen, right?
2) while I'm at it, do I read right that you don't need a fire stone to breathe fire? Just does base ruler damage? As does a water attack if there are no central water stones?
3) when there are 3 water in the center, water attacks seem very powerful. You can cause the enemy dragon to lose 3+1 stones - for a segment - leaving 3 in the center. If you're positioned well you can do the same again very next turn. Am I missing something?