I read this story on Yahoo news today.

31 cities’ tap water has cancer-causing hexavalent chromium, study says

The Environmental Working Group released a report Monday indicating that millions of Americans are regularly drinking hexavalent chromium, made famous in the film “Erin Brockovich” as a carcinogen, through their tap water.
The group — whose study was first reported in a story Sunday by the Washington Post’s Lyndsey Layton — tested water from 35 U.S. cities and found that samples from 31 cities contained hexavalent chromium. The highest concentrations were found in Norman, Okla.; Honolulu; and Riverside, Calif. The substance had been a widely used industrial chemical for decades and has evidently leached into the groundwater in many areas.
[Related: Drilling ban follows concern over flammable water] The EWG report states:
“Despite mounting evidence of the contaminant’s toxic effects, the U.S. Environmental Protection Agency (EPA) has not set a legal limit for chromium-6 in tap water and does not require water utilities to test for it. Hexavalent chromium is commonly discharged from steel and pulp mills as well as metal-plating and leather-tanning facilities. It can also pollute water through erosion of natural deposits.
“The authoritative National Toxicology Program (NTP) of the U.S. Department of Health and Human Services has said that chromium-6 in drinking water shows ‘clear evidence of carcinogenic activity’ in laboratory animals, increasing the risk of gastrointestinal tumors. Just last October, a draft review by the EPA similarly found that ingesting the chemical in tap water is ‘likely to be carcinogenic to humans.’ Other health risks associated with exposure include liver and kidney damage, anemia and ulcers.”
[Related: Leaking ice raises tricky climate issue] Drinking-water supplies all over the country are increasingly tainted by chemicals used in natural gas drilling. And Erin Brockovich, for her part, told the EWG that she’s rather astonished to find that hexavalent chromium is still a prospective health threat in so many communities.
[List: America’s most polluted cities] “It is sometimes difficult to understand why I still have to warn the public about the presence of hexavalent chromium in drinking water 23 years after my colleagues and I first sounded the alarm,” Brockovich told the EWG. “This report underscores, in fairly stark terms, the health risks that millions of Americans still face because of water contamination.”
The list of cities found to have hexavalent chromium in the municipal water supplies are as follows:
• Honolulu, HI
• Bend, OR
• Sacramento, CA
• San Jose, CA
• Los Angeles, CA
• Riverside, CA
• Las Vegas, NV
• Salt Lake City, UT
• Scottsdale, AZ
• Phoenix, AZ
• Albuquerque, NM
• Norman, OK
• Omaha, NE
• Madison, WI
• Milwaukee, WI
• Chicago, IL
• Ann Arbor, MI
• Louisville, KY
• Cincinnati, OH
• Buffalo, NY
• Syracuse, NY
• Pittsburgh, PA
• Villanova, PA
• Boston, MA
• New Haven, CT
• New York, NY
• Bethesda, MD
• Washington, DC
• Atlanta, GA
• Tallahassee, FL
• Miami, FL

source: http://news.yahoo.com/s/yblog_thelookout/20101220/ts_yblog_thelookout/study-tap-water-in-31-cities-contains-cancer-causing-chemical