I was also initially worried about the idea of inhaling a "fluid." But as a vapor of two years myself I would like to
throw some points out that will hopefully put this concern to rest.
a) look at the volume.
we think if this as "liquid" but even if you hit a 2 mil clear carto over a day you are actually inhaling less liquid then water vapor in an average shower within 15 minutes.
b) Its not all water.
As others have mentioned the main liquid is PG or VG. Both of these are essentially single molocule sugars. Essentially what this means is that the body can take and process this directly from the blood stream, and is not likely to "build up" in the lungs.
c) If inhaling PG was dangerous on a long term level we'd be seeing Carnies and stage dancers dropping from exposure.
Just some points to think about
-Ed