I haven't updated the spells yet, but I revised the slam/grapple to include the whelm effects, I adjust the AC of the elder water, and I removed untethered from the traits.One note on the big water elementals. So I've also assumed the base water elemental just "took 10" on its athletics check for the grapple escape DC (as its normally an opposed athletics check.
The bigger elementals actually have proficiency in athletics, so should the escape DC be adjusted accordingly?
I am actually making a really epic fight coming up involving a lot of water elementals (ancient, elder, and regular), so I've been stating things up. Here are just my general notes as I've been making the encounters, and then I'll let you know how it actually went.
1) The Elder's AC is 13 but the other elementals are 14. I've made it 14 just to make it easier for me to run, that way everything has the same AC.
2) Comparing the water elemental to the air one, the spells are much weaker in general. One thing I did is add in Control Weather to the Ancient Water (precipitation only). I really liked this massive storm as being the warning that these elementals are coming. I also gave them acid splash (11th level) as an at-will (but bludgeoning instead of acid damage). This gives them a little more to do with their bonus action cast, as control water doesn't always come up. Lastly I gave them Vitriolic Sphere (bludgeoning instead of acid) instead of watery sphere. I figure the elementals attacks already have the grapple and can't breath motiff, so watery sphere is just more of the same. Vitriolic offers some area damage and most importantly, some range....which is a weakness of the water elemental, so I thought to beef that up a bit for the bigger ones.
3) Considering that the higher elementals get saving throw advantage and advantage against incapacitation...I'm just going to add Incapacitation to their list of immunities. They already have so many others that I think it fits right in, and its one less things for me to think about saving throw wise.
4) The Ancient has the ability to grapple on its slam. I am pondering using the same mechanic as whelm, once your grappled your just in the elemental, taking damage and unable to breath. Was curious what the intention was?
I will get to the spells later.