PHOENIX — Arizona is one of three states in which tap water has the highest average statewide levels of chromium-6, the carcinogen made popular by the 2000 “Erin Brockovich” movie.

The Environmental Working Group’s new report also shows Phoenix leads the nation’s largest cities for tap water that contains the cancer causing chemical.

The report found 79 of 80 samples from around Phoenix (taken by the city of Phoenix for an EPA study), contained “by far the highest average level” of chromium-6 of any major U.S. city.

“That number is misleading, because it doesn’t take into consideration that chromium-6 comes from mostly our ground water system,” said Troy Hayes, assistant director of the city of Phoenix Water Services Department.

“Ground water only makes up 2 percent of the water in which we distribute every day,” he said.

Hayes maintained the water in Phoenix is completely safe.

But of all major cities, why are only Phoenix’s numbers “misleading?”

“It’s skewed in the sense that we’re so heavily dependent on surface water here that has hardly any chrome in it, that it dilutes that number down,” he said.

But David Andrews, the co-author of the study, said the mixed water has chromium-6 levels that are worrying.

“I don’t think we need to run away (from the water), but it definitely raises some questions and it definitely raises some concerns,” he told KTAR News 92.3 FM’s Bruce St. James and Pamela Hughes.

The city of Phoenix issued a response to the study that can be read here.

“For the city of Phoenix, one test of a ground water well, and one test of a surface water well don’t necessarily count as equal,” Hayes said. “When you put in 98 percent surface water, and only 2 percent ground water.”

Andrews said people who are worried about chromium-6 and other contaminants in their drinking water should consider installing a filtration system.

“In my home, I would add slightly more filtration to clean it up more,” he said.

The study also showed Arizona has one of the highest average statewide levels, highlighting high levels of the carcinogen in the water of Maricopa, Yavapai and Mohave counties.