Considering the power boost the base races got in PF, it's not hard to make Genasi balanced against them with no level adjustment or anything. Here's my attempt at such...
Water Genasi
+2 Con, +2 Wis, -2 Cha
Medium-sized Humanoid
30 ft base speed
30 ft swim speed
Cold Resistance 3
Darkvision 60 ft
Obscuring Mist 1/day as a Druid of their Character Level
Drench
+1 racial bonus on saving throws against water spells and effects, increasing by +1 every 5 levels
Water Breathing
Automatic Languages: Planar Trade, home region.
Bonus Languages: Any (except secret
languages, such as Druidic).
Added a +2 Wis (seemed to fit water, even if a little odd for Genasi), lowered the cold resistance, and replaced Fog Cloud with Obscuring Mist.
Now, the whole water = cold thing can be debated, and if someone has a good suggestion of a way to replace it, let me know.
I've been considering replacing the incremental save bonus with a flat +2 from the beginning on all the genasi. Opinions?
I'm not sure how to handle Gith or Nathri without PF Psionics available, though I might give Nathri a try anyway. Expect an attempt at Shad, Chaonds or Zenythri as the most likely next one.