So I was picking spells for my Lv1 Cleric and encountered "Air Bubble", that is a Reaction spell. From the wording I felt like I could only cast it as a Reaction, so if I was out of range when the Fighter was submerged into water or I had used my Reaction on that turn, I couldn't cast it at all on him while he remained under water (because the triggering of the Reaction is him ENTERING an enviroment where he can't breathe).
That didn't make sense, so I started to look for some Ruling/Wording in the book that specified that I could cast a Reaction Spell as if it were an Action Spell.
The closest I got was in Page 195 on the "Spellcasting Actions". It reads as follow:
"As noted in Cast a Spell, some specific spells let you turn spellcasting actions into reactions or free actions."
The key wording being that it allows you to "turn" them from Actions into Reactions. Nowhere else is this stated/explained (neither on the "Cast a Spell" section that is mentioned and right next to the text I quoted).
I think the book needs a cristal-clear ruling that states (directly, not implied) that you can always cast a "Reaction Spell" using a normal Action with the same Spellcasting traits.
On a side note, I don't see why I should be able to cast this as a Reaction when an ally ENTERS an environment where he can't breathe, but not on the next turn (still as a Reaction) while an ally IS INSIDE an environment where he can't breathe.