A BBC investigation has found that bottled water from a well in Mecca is being covertly marketed to British Muslims, even though it's known to contain dangerous levels of arsenic. The discovery of secret caches of "Zam Zam Water" creates a delicate enforcement situation for British authorities, who must crack down on a black-market product that could harm the very people who see it as sacred. "People see this water as a holy water," environmental health officer Dr. Yunes Ramadan Teinaz tells the BBC. "They find it difficult to accept that it is contaminated, but the authorities in Saudi Arabia or in the U.K. must take action." The Zam Zam Well plays a central role for pilgrims to Mecca, where it has pumped water for centuries, just a few dozen feet from Islam's holiest site, the Kaaba. Though pilgrims are allowed to take small amounts home with them, exporting it in large quantities is illegal. But the iconic well's marketing power isn't just limited to its water. Iran's Zam Zam Cola has swelled in popularity over the past decade in Arab nations thirsty for symbolic alternatives to Coca-Cola and Pepsi.