"It's impossible to say one way or another that bottled water is safer than tap," he says. "There have been a number of instances in recent years where companies have had levels of arsenic, for example, that did not meet federal levels for drinking water."

In fact, of the 130 brands of bottled water studied by Consumer Reports, 11 were found to contain arsenic -- in some cases above federal limits.

Last year, Dr. Pepper pulled one of its bottled water brands, Penafiel, from the U.S. market because of high arsenic levels. And in 2016 and 2017, Whole Foods recalled about 2,000 cases of one of its bottled water brands, Starkeys. High arsenic levels were again to blame.

Of course, municipal water systems can have problems, too. Last summer, Newark handed out free bottled water after tap water in the city was found to contain high levels of lead.

Determining the quality of bottled water isn’t always easy. Municipal water systems have to publish water quality test results each year, but bottlers only have to test water, not disclose the results. You can ask for them, but they won’t always tell you.

"We tried to identify as many bottlers as we could this year that were operating. I found just north of 230," says Felton. "But we were only able to obtain test results of just over half of those."

One study found that in most cases, bottled water is as safe as tap water. But that's because two-thirds of the time -- it actually is tap water. It may be run through a filter or simply sold as-is, in a bottle.