Dangerous levels of the carcinogenic chemical chromium-6 can be found in the tap water drunk by 218 million Americans, a new report has revealed.

The toxic chemical was brought into the spotlight by Erin Brockovich when she fought a power company accused of leaking the chemical into tap water supplies in California.

On Monday, figures released by the Environmental Working Group showed 50 states are exposed to unsafe levels of chromium-6 or hexavalent chromium.

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Renowned activist Erin Brockovich fought Pacific Gas and Electric Company over allegedly leaking chromium-6 into water supplies in California

Over 75 percent of 60,000 water samples gathered between 2013 and 2015 contained levels of chromium-6 above 0.02 parts per billion.

California state scientists say that 0.02 is the threshold which chromium-6 begins posing a cancer risk over 70 years of consumption.

The state with the highest amount of chromium-6 in its water is Phoenix - with almost 400 times the amount that the California scientists set as a health goal.

'This is quite shocking, to be honest,' Brockovich told Newsweek, as she explained never knew the issues was so widespread.

Chromium-6 is a naturally occurring toxin that is also manufactured for use 'in steel making, chrome plating, manufacturing dyes and pigments, preserving leather and wood and, as in the Brockovich case, lowering the temperature of water in the cooling towers of electrical power plants', EWG explained.

A 2008 National Toxicology Program study found that mice and rats who drank chromium-6-laced water developed stomach and intestinal tumors.

Phoenix, Arizona, has the highest amount of chromium-6 in its water supply, with almost 400 times the amount that the California scientists set as a health goal

This table from Environmental Working Group shows the places with the unsafest levels of chromium-6 or hexavalent chromium

This led the United States Environmental Protection Agency to classify oral exposure to chromium-6 as 'likely to be carcinogenic' in a draft risk assessment, EWG reports.

Bill Walker, co-author of the EWG report, told CNN: 'Americans are exposed to dozens if not hundreds of other cancer-causing chemicals every day in their drinking water, their consumer products and their foods.

'And what the best science of the last decade tells us is that these chemicals acting in combination with each other can be more dangerous than exposure to a single chemical.'

EWG want the EPA to set new standards on chromium-6.

On Tuesday the agency announced they are funding six universities to work with local communities to better understand the economic value of water quality.

'Chemical and microbial contaminants continue to reduce the quality of our water – and often at a rate that outpaces water quality improvements from regulatory actions.

'The research grants announced today will help communities and experts conduct benefit-cost analyses for actions that protect our waterways,' a statement said.

The EPA also vowed to carry out a 'comprehensive evaluation of potential health effects' of chromium-6 and release a draft assessment in 2017, USA Today reports.