Risky Water: 5 Most Incredible Discoveries of the Week Also: a surprising find about fitness trackers By Newser Editors, Newser Staff Posted Sep 24, 2016 5:23 AM CDT 4 comments Comments (AP Photo/Patrick Semansky) (Newser) – A disturbing find about common tap water and an intriguing one about a famous shipwreck were among the biggest discoveries of the week: That Chemical Erin Brockovich Fought? You're Likely Drinking It: If chromium-6 rings a bell for some odd reason, that reason is likely Erin Brockovich, who famously helped secure a massive settlement for the Hinkley, Calif., residents exposed to the heavy metal. Now a new report suggests you've been exposed, too. The Environmental Working Group analyzed EPA-ordered samples of drinking water to estimate that 218 million Americans—some in every state—are being exposed to unsafe levels of the probable carcinogen. It's especially bleak for Phoenix. We All Come From Single Wave of African Migrants: Scientists agree that modern humans originated in Africa around 200,000 years ago, but they have long debated on exactly when and how we spread across the globe. Now, a trio of studies based on DNA evidence posits that virtually all people living today are descended from the same wave of humans that left Africa between 50,000 and 80,000 years ago. There's one tiny exception. Antikythera Shipwreck Yields Human Remains: The Antikythera shipwreck has yielded many exciting results since its discovery off Greece a century ago, most notably the world's oldest known computer. Now divers say they've unearthed surprisingly well-preserved human remains, raising the hope that enough DNA has survived to be sequenced. One scientist wonders if they've found the owner of that old computer. Your Fitness Tracker May Be Working Against You: For those looking to lose weight, a two-year study suggests that wearing a fitness tracker helps. What surprised researchers, however, is that not wearing one seems to help even more. The difference ended up being a not-insignificant 5 pounds, and researchers have a theory about what's going on. Want Lower BMI? Pot Might Help: People who smoke weed on a daily basis tend to have slightly lower body mass indexes than people who don't, and while researchers say they're not suggesting that people take up regular marijuana smoking, they're keen to understand the mechanism at play. And, yes, the researchers are well aware of the munchies factor. Click to read about more discoveries.