Has it actually been over a year already? When I first started I must admit I was a bit nervous about heading out in such uncharted waters, but this thread has really been picking up steam since then.
But enough talking: let's see if these mephits are worth their salt!
Salt mephits, like their earthy cousins, are slow fliers but possess a fair amount of muscle to make up for it. Their breath weapon is identical to the dust mephit's, and fast healing is similar to theirs but without the ability to function in dusty environments.
The 1/day SLA is the underwhelming ability to suck moisture out of living creatures that will be bad at first and useless after. This is fully compensated by the hourly SLA, though. Glitterdust is great and will always be great, and three rounds of it are typically enough to win any fight.
+1 LA, but reasonably close to +0.
Again we note how fire creatures get the short end of the stick: steam mephits have the same low ability scores as the fire and magma versions.
Their SLAs are Blur and weak blasting. Their fast healing functions in boiling water or warm and humid areas. The breath weapon is the fire penalty version.
Last of all, the water mephit. These, too, can swim. Their breath weapon is a cone of non-penalizing acid (unlike the ooze mephit's cone of penalizing acid), their SLAs are Stinking Cloud 1/day and Acid Arrow 1/hour (woooo, 4d4 damage that isn't even applied all at once). Fast Healing functions in rain or when the mephit is up to its waist in water.
Stinking cloud is really the only thing this one's got going for itself over other mephits (and even then, ooze's just plain better). +0 LA.
Coming next: merfolk.