Summoned water Elementals. Can I swim in?

[kyubi3009]

In the event I summon a water elemental of size large or above could I just jump inside and use the water elemental body (wich is made of water) as if submerged in a body of water applying all the rules relative to underwater combat including total cover?

[LordKailas]

IMO it should be treated as if the water elemental had used swallow whole on you. So, you would also gain the grappled condition along with it's associated penalties.

[Shiroi]

I'd say there's some interesting effects going on here. I agree with the grappled condition, I think if the elemental moved you'd need to make swim checks to keep up and if it fought in any significant capacity you'd take bludgeoning damage from being inside the roiling mass. You'd be holding your breath, couldn't do much between grappled and swimming and being tossed around and can't speak for verbal or stay put long enough to use somatic, your attacks also have miss chances and penalties out the wazzu...

You'd make yourself useless and stop the water elemental from being useful too. At this point you may as well use aqueous orb and save yourself the bother of making it sentient. It's a strictly defensive tactic that might possibly save you from a hail of fireballs and such but will be at best buying time.

Tl;Dr Cool idea, you're better off using a wall of force and calling it a day.

[kyubi3009]

And what if I'm a merfolk with natural swim speed and underwater breathing? I was thinking of using this similar to Seamantle but with the total cover benefit. Note I did consider doing the same with Aqueous orb but unlike the elemental said orb automaticaly inflict non lethal damage id rather not take albeith easily negated with fluid form.

The elemental doesn't need to move while I bombard people with non fire (or lightning) spells from inside its belly. I'm considering the elemental as a stationnary huge size mobile aquarium of pure (albeith living) water for my personnal swimming conveniance.

I personnaly do not think a water elemental capable of performing swallow whole due to its ability to use Vortex instead. And by all logic a body of still water isn't exactly capable of grappling.

[The Sideromancer]

Consider using this spell instead.

[kyubi3009]

The Sideromancer wrote:

Consider using this spell instead.

Globe does not create water it only calm the water around you. That's been my first option until I discovered it would not work.

[Dave Justus]

Per the rules, the answer is no. You can't share the space of another creature.

Beyond that, an elemental isn't really just water, they are made out of 'living water' whatever that means but certainly whatever it is it is not like regular water. Water wouldn't take any damage from being hit with a sword for example. Unlike regular water, the living water of a water elemental also holds its form and can move as it desires.

Certainly being inside an elemental (if it could be done) would give you total cover, but it would also block any line of effect from you to outside of it, its status as a creature would be the rules you would use, not the environmental rules for water.

[Shiroi]

I could see this actually with those stipulations. It's a still body of water, you have a swim speed and can breath, you'll have to stick a hand out to cast the spell similar to someone using glide to do this with earth.

If you don't also stick your head out of the water I'd say the curvy, ripply surface is going to make it very hard to accurately see more than a few feet, and if you do someone's going to hold an action to ping you with an arrow (with a much lower miss chance) when you pop out to cast. You can still use fire spells in this case, since the hand it outside, but lightning could be risky and might backfire.

I can't imagine this being particularly healthy for the elemental either, it's not like it has organs but it takes damage when foreign objects enter it (like swords) so I doubt having a full sized mer-person in it will be a long lasting condition before it dies.

Occupying the same space as a creature was mentioned, and I can see a case there as well to shut this down, that's going to come down to DM discretion since the entity isn't perhaps using all that space in a physical sense and it is an ally.

This is sadly reaching the level of houserule, Homebrew, and DM discretion. You're playing with the rules in a way they aren't meant to and letting real world physics bleed in, so I'm going to step out with my last bit of advice: the DM will absolutely be the last say in this kind of thing and it's going to depend on how often and in what circumstances you want to use this trick and how balanced and fair it is to the party and the story.

[Shiroi]

I don't like to double post but it's been too long to edit that one reasonably.

For an alternative to this, you may consider a level in synthesist summoner to 'summon a water elemental you can ride in'. If you're more interested in the flavor than anything else, this should work fine.