Thus far, the only other situations shown to increase a bender's ability are:

- The full moon strengthens waterbending.  This could arguably fall under the moon simply being out, but this is the pinnacle of that circumstance. (i.e. bloodbending can only be performed under a full moon)
- Waterbending is greatly increased while in the [Spirit Oasis][1].  Water from the Oasis also has unique properties that make it a powerful tool.


  [1]: http://avatar.wikia.com/wiki/Spirit_Oasis#axzz1kxZz8Zx1