Frequently Asked Questions: Chromium in Water

Is Madison tap water safe to drink?

Yes. Madison water is routinely tested for more than 130 potential contaminants, including both regulated and unregulated substances. Our extensive testing confirms that we meet or exceed all federal and state drinking water standards.<.p>

What is chromium-6 and why is it in our water?

Chromium-6 is an element that is commonly found at low levels in drinking water. It can occur naturally in the ground but may also enter drinking water sources via industrial pollution. Research conducted in collaboration with the Wisconsin Geological Survey strongly suggests a natural origin of the chromium-6 found in Madison’s drinking water; it is not likely caused industrial pollution. Chromium-6 has been detected at low levels (less than 2 ppb) in 14 of Madison's 22 wells.

Is chromium-6 dangerous?

Chromium-6 is known to be a potent carcinogen when inhaled. It was recently found to also cause stomach cancer in laboratory mice and rats when they were exposed to extremely high levels in drinking water. Right now, there is no federal regulatory standard for chromium-6, although the State of California has enacted its own regulatory limit of 10 ppb.

How do our rates of stomach cancer compare to the rest of the state and nation?

The level of chromium in our area's drinking water has remained steady at least since the 1970s, yet rates of stomach cancer in Madison have declined over the same period. The statewide rate of stomach cancer is well below the national average (3.8 per 100,000 people) and Dane County has one of the lowest rates in the state (2.5 per 100,000 people).

Could coal ash dumped on the Isthmus decades ago be a source of the chromium-6?

It's unlikely that coal ash is contaminating Madison's water with chromium-6. Our wells nearest to known coal ash deposits on the Isthmus have some of the lowest levels of chromium-6 in the city. One has never shown detectable levels, and the other has shown trace levels of .03 parts per billion, although most of the time it is not detected there at all.

Have chromium levels in Madison water increased?

No. The chromium-6 found in Madison's water is likely naturally-occurring and has been present in the area's water for many generations. Total chromium levels have been measured at Madison wells since at least the early 1970s, and the levels are relatively unchanged since that time. The techniques and the methods for measuring chromium may have changed, but the concentrations have not.

Chromium-6 was the carcinogen made famous by the movie Erin Brockovich. Hinckley, California residents were awarded a multi-million dollar settlement from Pacific Gas & Electric, a company that used chromium-6 to prevent rust in cooling tower water at its compressor station. Wastewater from the station percolated into the groundwater, affecting an area approximately two miles long and nearly a mile wide. Concentrations in groundwater monitoring wells in Hinckley have measured over 500 ppb.

What is the difference between total chromium, chromium-6, and chromium-3?

Chromium occurs in the environment and drinking water sources in two principal forms:  trivalent chromium (chromium-3) and hexavalent chromium (chromium-6). The sum of all chromium in a sample is called total chromium. Chromium 3 occurs naturally in food and is an essential dietary nutrient while chromium-6 is a more toxic form of chromium.

Chromium can transform from chromium-3 to chromium-6, and vice versa, depending on the physical and chemical environment. For example, industrial releases of chromium-6 are often converted to chromium-3 after being deposited into the soil.

What is the current water quality standard for chromium?

Currently, there is no federal or state regulation for chromium-6. The federal government regulates only total chromium and the maximum contaminant level (MCL) is 100 ug/L or 100 parts per billion (ppb). When the regulation was established, it was assumed that all chromium in drinking water was chromium-6 and the MCL of 100 ppb was protective of human health.

The EPA has been collecting nationwide occurrence data for chromium-6 in drinking water. The agency plans to use this information to determine whether a regulatory limit specifically for chromium-6 should be established.

What are the total chromium levels for Madison wells?

All Madison wells are tested annually for total chromium. The levels range from below detection to a little over 2 ppb and are relatively unchanged in the over thirty years of test results we have. These levels are well below the current regulatory limit of 100 ppb. Nearly all the chromium found in Madison drinking water occurs as chromium-6.

Why doesn't the EPA require testing of chromium-6?

When the total chromium standard was established in 1992, chromium-6 was classified as a carcinogen for inhalation (an occupational hazard associated with inhaling chromium dust in metal processing facilities) but not for consumption in drinking water. At that time, it was believed that any chromium-6 ingested in drinking water was converted to chromium-3 by stomach acid. However, recent studies on mice and rats have raised questions about this earlier assumption. The EPA is currently reviewing the science to determine (1) if water utilities should be required to test for chromium-6 in addition to total chromium, and (2) whether the drinking water standard for total chromium should be adjusted, or whether a new standard should be established for chromium-6.

In the interim, US EPA recommends that drinking water systems monitor for chromium-6 to “better inform their consumers about the levels chromium-6 in their drinking water, evaluate the degree to which other forms of chromium are transformed into chromium-6 in their drinking water and assess the degree to which existing treatment is affecting the levels of chromium-6.” Madison has tested each city well for chromium-6 at least twice annually since 2011.

Why is the EPA reviewing its current standard for chromium?

New research on mice and rats and data collected from China suggest that chromium 6 in drinking water may cause stomach cancer in humans.

Do any water utilities currently test for chromium-6?

In January 2011, Madison began a comprehensive monitoring program for chromium-6. Other utilities in the state, including Milwaukee, Watertown, and Beloit, have tested for chromium-6 or are planning to do so.

What is the Madison Water Utility doing about the issue?

The water utility has begun voluntarily testing all its municipal wells, and we worked with the Wisconsin Geological Survey to determine the source of chromium-6 in our drinking water.
Madison Water Utility is also a participating (and funding) utility in a Water Research Foundation study examining the sources, fate, and treatment of hexavalent chromium.

How often will Madison water be tested for chromium, and where can I find the results?

The water utility began voluntarily testing for chromium-6 in 2011 and plans to test each well twice each year. Test results are reported on our website and through the Drinking Water Quality listserv, which you can join at

Where can I find more information about chromium-6?

Websites of the following organizations provide additional information on chromium-6 in drinking water with links to more information:       

United States EPA – Chromium in Drinking Water

California Dept. of Public Health – Chromium-6 in Drinking Water: MCL Update