I'm afraid I can't be of much help on this subject since the reality is that not much worth while research exists on the subject and what is out there doesn't really have enough depth to draw an informed opinion on. The various links i've posted on the risk factors associated with tobacco consumption in general are easy enough to dig up but I don't feel like dredging them up for the hundredth time since it seems no one bothers to read them.
Our valued German compatriot PC Serve has a fairly topical thread found here: http://www.hookahpro.com/forum/showthread.php?t=10991
which doesn't really address the matter at hand and is far from comprehensive but it has some utility. What I can say with a great deal of certainty is:
1) Given the incredibly poor and heavily biased material that exists on cigarettes any sort of base line measure for making a comparison with moassel consumption is almost impossible given the vast problems of forming sensible control and experimental groups and the huge variability of narghile design, smoking method, coal characteristics and moassel composition.
However, one can safely say that cigarette consumption at the level of a pack a day increases one's life time risk of lung cancer and a variety of cardio-pulmonary diseases by a factor of X4-X8 depending upon which studies you reference in Occidentals but less so with other races. Bottom line is that the intervening, contributing and compounding variables in narhgile use are simply far to varied and complicated to be handled adequately in a few studies and the political/social/economic/religious baggage is such that I doubt much will be done to rectify the matter.
2) Water is not a great filter medium although diffusers help a good deal. So the truth is that all smoke will contain solids but the best way to reduce that problem is to clean your narghile and hose frequently and carefully.
3) All moassel (save the hard to find old school stuff that isn't imported often) uses glycerin to add a bit of sweetness and increase smoke production and prop. glycol is not used in any moassel that I am aware of. Glycerin is a simple sugar and the effects of inhaling vaporized glycerin is very much an unknown health risk.
4) By far the most dangerous aspect of smoking moassel is the CO created by the coals. I've done some half assed studies on my own using mass spectrometry and I found that the natural coals resulted in far less CO then QLs. I also found that the height of the narghile had a lot to to do with CO content but that mainly smoking method is what matters most. The matter of smoking method is something that has been confirmed in the Sullum text I cited as well as Frenk's text on nicotine absorption and addiction.
5) Inhaling smoke is a bad idea since it has a significant, although heavily debated, set of risk factors. Since no human has taste buds in the lungs or throat I don't see the point in haling since to me smoking is about taste, craftsmanship, comradery and taking time out to absorb your surroundings.