It only applies to Watercannon's additional damage, just like Water Alchemy, Alchemy Mastery and Cylinder Ego Enhancement, So naturally, Fire Alchemy Efficiency reforge sucks too.
Did some testing
Single charge - without reforge
698
687
700
700
700
700
691
688
698
700
700
Single charge - with lv19 water alchemy efficiency boots
729
719
736
717
731
737
737
730
I also tested with full charges, not much of a difference at all.
- Rank1 Watercannon, Alchemy mastery Water Alchemy, Guard Cylinder Mastery.
- 52 Water Alchemic Damage + 1223 Mana
- Normal Cylinder and Guard Cylinder
- No gear
Just thought I'd post this on Nation.