[Squirrelloid]

Water has a number of good spells for UW combat or just combat in general:

Shark Attack/Summon Sharks, Frozen Heart, Water Ward have already been mentioned. Friendly Currents its generally better to get from the item.

Numbness can be amazing when spammed (admittedly also doable via item, but its worth casting without one).

Encase in Ice is a pretty good anti-SC spell. Worst-case scenario you can freeze an SC until they auto-die on turn 75.

Water has some good summons as well, including Clay Men (in enchantment), Sea Serpents, Naiad Warriors, and Asp Turtles for UW use. (On land it has Catoblepae and winter wolves - both of which i've used). It also has Naiads and Kolkythiads (Streams from Hades), the former is good for bootstrapping nature, and the latter is great for bootstrapping in death or gaining death casters *while using water gems*.

Bone melter would be good if its targetting was better or it was easier to cast.

And of course the acid spells are a good supplement to the cold spells for non-UW combats, since they aren't resistable.

The problem is that many of the good water spells are crosspath, and thus require you have the right other paths to use with them. Meaning any given water nation will have access to some but not all of the decent to good water spells. Pure water spells that are good are mostly useable UW though.