Effects of water filtration on marijuana smoke: a literature review
http://www.ukcia.org/research/Effect...uanaSmoke.html

The water did trap some THC, as well as other psychoactive compounds, however, most of the THC present in the marijuana passed through the water pipe unchanged. Pharmacological tests (in mice) revealed that some of the water-trapped marijuana compounds were responsible for producing catatonia and for suppressing spontaneous motor activity. In contrast, the water-filtered smoke itself did not affect spontaneous motor activity and did not induce catatonia, though it was richer in THC. These results indicate that water filtration removes some behaviorally active compounds in preference to others; this may be important when comparing the therapeutic effects of whole marijuana smoke to water-filtered smoke.
Maybe, those with a family history of schizophrenia should be recommended to use a bong.