Chromium 6 and drinking water

What is chromium?

Chromium is a metal found in rocks, soils, plants, water and animals. The most common forms of chromium in the environment are trivalent (chromium 3), hexavalent (chromium 6), and the metal form.

What is chromium 6 and why is it of interest regarding drinking water quality?

Chromium 6 is one of the forms of chromium; it is the most oxidized form.  Chromium can convert between chromium 6 and chromium 3 depending on the conditions of the environment.

The US Environmental Protection Agency (EPA) is currently reviewing results from a long-term animal study, which suggests that chromium 6 may be a human carcinogen if ingested, and other recent research.

For the American Waterworks Association’s information on chromium 6 including occurrence, health effects, regulatory aspects, and treatment technologies, please click here.

How does chromium get into water?

The major source of chromium 6 in drinking water is natural chromium present in some types of rock. There are also industrial sources of chromium, but OWASA’s watersheds are highly protected and, as far as we know, do not currently contain any of these sources.

What are the limits on total chromium and chromium 6 in drinking water?

The EPA limits total chromium (i.e., all forms of chromium) in drinking water to a maximum of 100 parts per billion (ppb). This level was set assuming all chromium detected is in the form of chromium 6.

Currently, there are no federal limits for individual forms of chromium in drinking water (such as chromium 6), but states are allowed to set regulations that are stricter than federal regulations.

California is the only state which regulates chromium 6 with a limit of 10 ppb. 

California has adopted a Public Health Goal (PHG) for chromium 6 of 0.02 ppb. 

A PHG is not a regulatory requirement and therefore compliance is not enforced. The California Water Board's Fact Sheet on the PHG says in part that “A drinking water sample with a detection of [chromium 6] above the PHG of 0.02 ppb does not necessarily represent a public health concern. The PHG is based on a cancer risk of no more than one case of cancer per one million people. The PHG tries to account for persons at three different stages in their lives by including protection factors to account for age and by applying higher rates of water consumption in their calculation … The California PHG represents the level of [chromium 6] at which no adverse health effects would be anticipated over an entire lifetime of exposure to the most sensitive population. So, a PHG is not a boundary line between a “safe” and “unsafe” level of a chemical, and drinking water is frequently demonstrated as safe to drink even if it contains chemicals at levels exceeding their PHGs.”

EPA’s Unregulated Contaminant Monitoring Rule

Through the Unregulated Contaminant Monitoring Rule (UCMR), the EPA collects occurrence and concentration data for various compounds which are or are suspected to be in drinking water, but currently do not have health-based standards under the Federal Safe Drinking Water Act.

The EPA is evaluating chromium 6 in a process which characterizes potential health risks based on the best available science. This evaluation will be a basis for deciding whether to adopt new or revised regulations. For more information, please visit the EPA webpage on chromium in drinking water.

OWASA’s testing for chromium 6

In testing from November, 2013 to August, 2014, we detected chromium 6 at levels ranging from less than 0.03 ppb to 0.06 ppb. Results from all participating utilities are available here

Results vary because utilities have different water sources and treatment processes. UCMR data is not intended to be used to draw any conclusions from comparing one utility’s results to another, but instead to provide the EPA with a more complete understanding of chromium 6 occurrence in drinking water nationally.

In anticipation of potential new Federal regulations, OWASA did a study in 2011 to determine the sources of the chromium 6 in our drinking water. We identified one of our treatment chemicals as the main source. We discontinued use of this product and reduced the levels of chromium 6 in our water by over 75%.

Does water treatment remove or reduce chromium 6?

Conventional water treatment has demonstrated the ability to remove chromium 3 from water, but does not remove chromium 6. Advanced technologies such as ion exchange, reverse osmosis, and microfiltration were successful in reducing chromium 6 concentration to less than 1 ppb in bench-scale and pilot-scale testing. (Please click here and visit Water Research Foundation, Web Report #4365, Microfiltration in the RCF Process for Hexavalent Chromium Removal From Drinking Water for additional information on these tests)

We continue to closely monitor scientific research and the EPA’s action on chromium 6 as well as other currently unregulated substances in drinking water, and will take action when necessary for the safety of our customers and our water.

For more information:

OWASA staff: Katie Harrold, Laboratory Supervisor at the Jones Ferry Road Water Treatment Plant, 919-537-4227 or


Water Research Foundation’s Web Report #4365, Microfiltration in the RCF Process for Hexavalent Chromium Removal From Drinking Water