Cancer-causing toxins are in the water that 200 million Americas drink every day, according to a new study by the Environmental Working Group.
Researchers say the City of Phoenix has the highest amounts of chromium-6 of any city over a million people nationwide.
Chromium-6 is a metal that can cause cancer when found in high concentrations in public drinking water.
Erin Brockovich brought the public health issue to light in the 1990's.
Phoenix water officials say chromium-6 is found on the rocks in our region, and well water has elevated levels. However, they say well water is only a small amount of the total water in the system, and their tests show levels are no more than 1.6 parts per billion when the water reaches homes.
California, which has the strictest requirements in the nation, allows for up to 10 ppb.
"Our customers are seeing a very safe product that we are putting out every day that has been treated and tested - that's well below any limit that anybody has," City of Phoenix Assistant Water Director Troy Hayes said.