@JeremyECrawford – Would a fireball cast under water vaporize the water in it's 20 foot radius?
— Lino Ciaralli (@ReaperCDN) February 27, 2017
Nothing in the rules causes a fireball to vaporize water. Magic ≠ physics. DMs may apply whatever magical/scientific logic they like. #DnD https://t.co/1mSjzxkxDF
— Jeremy Crawford (@JeremyECrawford) February 28, 2017