Thirty-six percent of Arizona’s population got their water from systems that violated the Safe Drinking Water Act in 2015, according to a new report.

The study, which looks at total violations and health-based violations, is by the Natural Resources Defense Council, or NRDC.

Arizona ranked among the five worst states for water systems with violations in three categories, including arsenic, radioactive material and carbon-based pollutants. But the Grand Canyon State did not show up in the worst five for health-based violations in any of those three categories.

A non-health based violation could be for failure to report data, or not testing for a particular contaminant, said Erik Olson, coauthor of the study, and director of the health program at NRDC.

“Water systems, on occasion, have been known to not test their water because they suspect there is a problem,” Olson said. “So we don’t know for sure what those non-health based violations might be hiding.” 

The study also found the Environmental Protection Agency did not take enforcement action on roughly nine out of 10 violations nationwide, and NRDC calls on the agency to strengthen its rules.

The EPA does not have a regulatory standard for perchlorate, which comes from jet fuel, and affects parts of Arizona, Olson said. 

“It has contaminated the Colorado River in the past,” Olson said. “It contaminates a lot of industrial and Department of Defense sites.”

The EPA is supposed to establish a standard for perchlorate in the next couple of years, Olson said.