We're doing a show in March in which the script calls for actors to smoke weed from a bong. Its a small theater which means authenticity is paramount. If it were a big house I would just use a bong that isn't loaded with anything and let the audience pretend there is smoke.

So I need a way for actors to smoke a real bong with something in it that generates "smoke" but it has to fit the following qualifications:

can't set off fire alarms (which I can disable but not legally)
can't contain things that are not legal in public places (so no tobacco)
doesn't force actors to inhale things that may be in violation of their personal health

I'm basically asking for ideas on building a prop bong that functions in an authentic way but doesn't break laws or set off fire alarms but still makes an authentic picture for the audience.

I have some herbal "ecstasy" cigarettes which are not technically legal, but would suffice unless I have a patron complain, or if I have an actor who refuses to inhale the smoke. I thought about rigging up a vape thing, but the vapor would likely just condense when it passes through the water in the bong.