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.

The ornate glass and metal water pipes are used for smoking an aromatic blend of tobacco, molasses and fruit known as shisha. A 2008 study of 3,770 students at eight universities in North Carolina found more than 40 percent had smoked a hookah at least once, only slightly lower than the percentage who had tried a cigarette at least once.

But researchers say the notion that water filters all the harmful chemicals in tobacco smoke is a myth. So, too, they say, is the idea that because hookah smoking is an occasional activity, users are inhaling much less smoke than cigarette users.

Many young adults are misled by the sweet, aromatic and fruity quality of hookah smoke, which causes them to believe it is less harmful than hot, acrid cigarette smoke. In fact, because a typical hookah session can last up to an hour, with smokers typically taking long, deep breaths, the smoke inhaled can equal 100 cigarettes or more, according to a 2005 study by the World Health Organization.

That study also found that the water in hookahs filters out less than 5 percent of the nicotine. Moreover, hookah smoke contains tar, heavy metals and other cancer-causing chemicals. An additional hazard: the tobacco in hookahs is heated with charcoal, leading to dangerously high levels of carbon monoxide, even for people who spend time in hookah bars without actually smoking, according to a recent University of Florida study. No surprise, then, that several studies have linked hookah use to many of the same diseases associated with cigarette smoking, like lung, oral and bladder cancer, as well as clogged arteries, heart disease and adverse effects during pregnancy. And because hookahs are meant to be smoked communally — hoses attached to the pipe are passed from one smoker to the next — they have been linked with the spread of tuberculosis, herpes and other infections.

“Teens and young adults are initiating tobacco use through these hookahs with the mistaken perception that the products are somehow safer or less harmful than cigarettes,” said Paul G. Billings, a vice president of the American Lung Association. “Clearly that’s not the case.”

Mr. Billings calls the emerging anti-hookah legislation a “top priority” for the lung association.

The organization is having some success, particularly at colleges where hookahs had become a fixture in dorms and fraternity houses. Louisiana State University, Baylor University, George Mason University, Lehigh University and others have expanded their antismoking policies to include hookahs in recent years.

Hookahs are a big part of the reason the University of Oregon will ban all tobacco products on campus as of next year, after years of complaints from students about secondhand smoke.

Students already are feeling the change. For Cassie Ramsey, arriving at college was a bit of a culture shock, because she had to leave behind her hookah pipe.

“I only smoke once, maybe twice a month now,” said Ms. Ramsey, a sophomore at Johnson & Wales University in Providence, R.I., where hookahs are not allowed in the dorms.

“It’s kind of depressing because over the summer I was a very avid hookah smoker,” she said, gathering at least once a day with friends for smoking sessions that would last up to two hours.

Local governments, too, are moving to stem rising interest in hookahs. Most of the anti-hookah laws now under consideration are intended to end exemptions in state indoor-smoking bans that allowed hookah bars to thrive. Such bans often contained exceptions for “tobacco specialty shops”; many hookah bars qualify as such by not serving food or alcohol. College towns in particular have reported a marked increase in hookah bars over the past five years.

“It was appalling to me when I first saw them springing up here in the Portland area,” Carolyn Tomei, an Oregon state representative, said of the more than 45 applications her state has received from hookah bars since its ban on indoor smoking went into effect in 2009. (Previously, there were five bars.)

These bars rely on theme nights and exotically flavored tobacco (passion fruit, “Sex on the Beach”) to market themselves to the college set, and many do not serve alcohol, making them an attractive destination for people under 21.

Ms. Tomei, Democrat of Milwaukie, a suburb of Portland, sponsored a bill to limit new hookah bars in Oregon; it passed the State House of Representatives in April and awaits a vote in the Senate.

Hookah bars have long been a mainstay of Middle Eastern life, and they are popular in American cities with large Arab populations, including New York, where Councilman Vincent J. Gentile, a Brooklyn Democrat, has introduced a bill that would prevent new hookah bars from opening next year and beyond.

The backlash against the crackdown has already begun. On Facebook, there are dozens of hookah interest groups, some aimed at protesting bans on hookahs.

“Why don’t they ban cigarettes from CT first, then we can get into the rest,” one Facebook member wrote on a page for people who oppose the hookah legislation in Connecticut. “I think this is just people being very judgmental.”