Julia Roberts put chromium-6 (and Hinkley, California) on the map in 2000 with “Erin Brockovich,” a movie based on real events that told the story of a small town battling a corporate giant over water supplies contaminated with the carcinogen.

But it turns out there are more than 100 public water systems in California, serving a million people, that may have unsafe levels of chromium-6, which has been linked to a number of health conditions. But what constitutes a safe level of chromium-6 contamination is currently up for debate after a judge in May ruled that California did not properly write a 2014 regulation that sets a maximum contaminant level for the element.

We take a look at what that decision means – from a regulatory and health perspective – and what happens next.