Underwater combat is never fun but for magic users it can be especially frustrating. Unless a character has Water Breathing or uses Alter Self they may find themselves in a situation where the DM rules that they cannot cast any spells with Verbal components–i.e. most of them.
At a gaming session my friends and I debated how effective most combat cantrips would be in an underwater environment.
We figure that most distance attack cantrips would be rendered useless: Acid Splash and Poison Spray would be diluted upon casting, Ray of Frost would turn the water immediately in front of the caster's fingers to a ball of ice, Fire Bolt and Produce Flame would be quenched immediately upon casting, etc.
But we weren't sure about a few Cantrips. Eldritch Blast would likely work as normal, but what about Sacred Flame which uses radiant energy? Would Shocking Grasp electrocute the caster as well as the target?
Best Answer
A spell only does what it says in the description
None of the spells you list, nor any spell you can cast, would be affected by being underwater except for the resistance creatures acquire against fire.
You can narrate this by justifying some magical force holding the energies of the spell together warding against water until the spell ends.
The full list of underwater combat rules can be found in the Player's Handbook (p. 198) which includes modifiers to weapon attacks but nothing regarding spells.