D&D 5E How do you handle casting spells underwater?

[Paraxis]

Verbal components don't work if you are gaged so following that logic they would not work underwater either. Maybe for underwater races with water breathing that learn the verbal parts of their spells in a way that works underwater.

As far as how it would effect the spells themselves, no info yet till DMG but traditionally I think lighting spells become spheres around the caster, wind magic doesn't work, and as noted in the underwater combat section anything underwater has resistance to fire damage.

 

[DracoSuave]

I have no problem with fireballs or lightning underwater as being fire or lightning or cold or whatever it is. The reason's simple--If evocation magic can displace air with fire, it can displace water with fire. It's magic--it breaks the rules of nature. It's also consistant--you evoke fire, fire happens.

However, with verbal components on most of that--that'll be the defining barrier to underwater magic. Pretty much the only way around that is sorcerer metamagic--and I'm okay with the class with the schtick 'You can break the normal magic rules' breaking the normal magic rules.

 

[Henrix]

Clearly a fit place for DM fiat.

At least disadvantage on fire spells. (Advantage on saves of course.)
Cold ought to freeze the water around the effect, though I'd leave exactly how to the DM.
Lightning might well be an area effect.

Spells relying on air and wind might work differently. I'd say it moves water around, but that is much slower.

Just having it make no difference seems utterly boring, and the world lessened. Letting the PCs think about it and plan for it is much more fun.

As for verbal components, I presume Water Breathing lets ju talk under water. You breathe normally. Your voice'd sound funny though.

 

[aramis erak]

As long as I've a lungful of air, I can speak underwater just fine. You might not be able to UNDERSTAND it due to bubbling, and I won't be able to take a second breath's worth... but I can easily speak for 3-5 seconds.

So, I'll allow ONE spell with a verbal component without an issue....

 

[77IM]

"Creatures fully immersed in water have resistance to fire damage." So that part's already taken care of in RAW.

I think I'd call for a concentration check to cast any spell under water. That seems like a good compromise between "you can't talk at all" and "nuh-uh! I can too totally talk just fine!"

Although I do like aramis's solution of, you can cast but then you start drowning...

 

[Paraxis]

This does bring up an interesting thought on verbal components.

Verbal( V )
Most spells require the chanting of mystic words. The words themselves aren't the source of the spell’s power; rather, the particular combination of sounds, with specific pitch and resonance , sets the threads of magic in motion . Thus, a character who is gagged or in an area o f silence, such as one created by the silence spell, can't cast a spell with a verbal component.

It seems the "particular combination of sounds, with specific pitch and resonance" is what is needed. So underwater, being drunk, having broken jaw, those few days after a tongue piercing, getting a few teeth kicked out of your skull all kinds of things could mess with a casters ability to make "particular combination of sounds, with specific pitch and resonance".

So yeah total DM judgment call depending on conditions, I would take it easy if they were going to spend a long time underwater for say the entire adventure, but if it was just an encounter or two I would probably make them think of some creative way around it, like using a make shift diving helmet or something.

 

[Sailor Moon]

Please don't interpret the inclusion of underwater fighting rules as some sort of acknowledgement spells should work differently too.

Instead interpret the absence of any special rules for underwater spellcasting as directly as possible.

Sorry but no. I'm not one of those "well if the book doesn't say I can't then I can" type of people.

Paraxis pretty much nailed it with regards to the verbal components part.

 

[Samurai]

We did a concentration check to cast underwater in our game, and I think that's a fair compromise.

 

[Paraxis]

We did a concentration check to cast underwater in our game, and I think that's a fair compromise.

That's fine if it works for you, but concentration doesn't work like that. Spells can either be cast or can not, concentration checks are for maintaining concentration spells. Which I would require of someone trying to do while fighting underwater if they couldn't breath water or had a swim speed.