Kevin Shapiro, a 20-year-old math and physics major at the University of Pennsylvania, first tried a hookah at a campus party. He liked the exotic water pipe so much that he chipped in to buy one for his fraternity house, where he says it makes a useful social lubricant at parties.

Like many other students who are embracing hookahs on campuses nationwide, Mr. Shapiro believes that hookah smoke is less dangerous than cigarette smoke because it “is filtered through water, so you get fewer solid particles.”

“Considering I don’t do it that often, once a month if that, I’m not really concerned with the health effects,” he added.

But in fact, hookahs are far from safe. And now, legislators, college administrators and health advocates are taking action against what many of them call the newest front in the ever-shifting war on tobacco. In California, Connecticut and Oregon, state lawmakers have introduced bills that would ban or limit hookah bars, and similar steps have been taken in cities in California and New York. Boston and Maine have already ended exemptions in their indoor-smoking laws that had allowed hookah bars to thrive.