The 66% water vapor came from a pdf (the last one) on a post from Roly.
It gets complicated
While I agree that you will have vapor from testing rebuildables - the actual second-hand vapor exhaled from a vaper is an entirely different animal and one that is more appropriate with regards to the effects on others.
One of the best studies I've seen is this one from Burstyn et. al.:
http://publichealth.drexel.edu/SiteData/docs/ms08/f90349264250e603/ms08.pdf
The problem is explained here:
"Monitoring of liquid chemistry is easier and cheaper than assessment of aerosols. This can be done systematically as a routine quality control measure by the manufacturers to ensure uniform quality of all production batches. However, we do not know how this relates to aerosol chemistry because previous researchers have failed to appropriately pair analyses of chemistry of liquids and aerosols. It is standard practice in occupational hygiene to analyze the chemistry of materials generating an exposure,
and it is advisable that future studies of the aerosols explicitly pair these analyses with examination of composition of the liquids used to generate the aerosols. Such an approach can lead to the development of predictive models that relate the composition of the aerosol to the chemistry of liquids, the e-cigarette hardware, and the behavior of the vaper, as these, if accurate, can anticipate hazardous exposures before they occur. The current attempt to use available data to develop such relationships was not successful due to studies failing to collect appropriate data. Systematic monitoring of quality of the liquids would also help reassure consumers and is best done by independent laboratories rather than manufactures to remove concerns about impartiality (real or perceived)."
Re: the bold - part of the study include evaluating other studies that didn't follow this procedure - like using smoke machines that didn't take into account the displacement that occurs in a vaper's lungs. These are the studies that say that the nicotine content of vapor is "10 times less" than that of a cigarette, but even that is grossly overestimated as Dr. F proved that the nicotine levels in
actual second hand vapor is nearly undetectable - lower than your regular 'trace amounts'. And even in some media accounts that report the '10 times lower than cigarettes' study, their headlines will read "Ecigarette vapor isn't entirely harmless - it also contains Nicotine!" or some such spin.
Another factor that isn't mentioned in some of the studies where they are actually studying second-hand vapor - the person exhales through some sort of a filter or similar contraption and only the substances that are captured by the filter are studied. While much of the 'air' and 'water vapor' is not captured. For example as stated in the Burstyn study:
"However, in a personal exchange with the authors of [37][July 11, 2013], (
this is a study that Burstyn was evaluating) it was clarified that the sampling pump drew air at 500 mL/min through e-cigarette for 10 min, allowing more appropriate calculations for estimation of health risk that are presented below.
Such misleading reporting is common in the field that confuses concentration in the aerosol (typically measured directly) with concentration in the air inhaled by the vaper (never determined directly and currently requiring additional assumptions and modeling).
This is important because the volume of aerosol inhaled (maximum ~8 L/day) is negligible compared to the volume of air inhaled daily (8L/min); this point is illustrated in the Figure."
This points to the fact that with ecigs the inhaled air through the air passages of the clearo/atty/carto is, along with the coil, what drives the vapor and it is a big percentage of the vapor compared to the eliquid that is vaporized by the coil. Studying the components of the eliquid itself can give one some indication of what
might be in second hand vapor OR studying the vapor from a smoking machine
may give you an even better idea, but the
actual second hand vapor from when the vaper exhales is truly what others should be concerned about and much of that is the air that is brought in from outside the ecig to start with, the water vapor as a result of the displacement and then the 'other stuff' as noted in many studies. But that other stuff is diluted much more as exhaled vapor than from analyzing the eliquid or even the vapor from a smoke machine.
That said, it
isn't all just 'water vapor' and 'air' but they make up a large part of second hand vaper.
