Back to top


What is chromium-6? 
Chromium-6, or hexavalent chromium, is a naturally occurring metal. It is also used in several industrial processes. There are other forms of chromium such as chromium-3, which is an essential nutrient and is sold as a dietary supplement. 

What are the health effects of chromium-6? 
Chromium-6 has been known to cause cancer in humans when inhaled. In scientific studies in laboratory animals, chromium-6 has also been linked to cancer when ingested. 

How does chromium-6 get into water supplies? 
Chromium-6 can occur naturally so it may be present in some groundwater aquifers. The types of rocks and soil associated with chromium-6 are known to occur in parts of Santa Clara County. Chromium-6 can also reach water supplies from industrial uses such as stainless-steel production, metal plating, and leather tanning. 

Is there a drinking water standard for chromium-6? 
No, but state limits on chromium-6 are expected by 2024. The State Water Resources Control Board (State Board) is considering a maximum contaminant level (MCL) of 10 parts per billion (ppb). One part per billion is equivalent to one drop of water in an Olympic size (660,000 gallon) swimming pool. MCLs are designed to protect public health and be feasible for water agencies to achieve.

The State Board has an MCL of 50 ppb for total chromium. This enforceable standard, which is more stringent than the federal limit of 100 ppb, remains in effect for drinking water. When an MCL is adopted for chromium-6, it will also be an enforceable regulatory standard that must be met by all public water systems. 

Has local water been tested for chromium-6? 
Valley Water has tested water from our three drinking water treatment plants, and has never detected chromium-6 at or above 1 ppb. This is the lowest reporting level currently available for a state accredited laboratory. 

Because it occurs naturally in soil and rock, chromium-6 is found more often in groundwater than in surface water. Chromium-6 has been tested at over 250 public water supply wells in Santa Clara County and was below the proposed 10 ppb drinking water limit in 99% of wells. Chromium-6 results ranged from non-detect to 19 ppb, and the median level was 2 ppb.

How do I know if my water contains chromium-6? 
Public water systems throughout the state have tested for chromium-6. If you get your water from a water company or city, they can provide you with the best information on the quality of water delivered to you. You can find contact information for your water retailer at If your water comes from a private domestic well, you may want to test your water for chromium-6. Valley Water recommends using a laboratory certified to test drinking water. A list of local certified laboratories is available at

Is there a filter that will reduce chromium-6? 
Yes, treatment technologies such as reverse osmosis can reduce or remove chromium-6. The State Board provides information on home treatment devices at

Valley Water recommends that you talk to the manufacturer or the company installing the system to confirm it will meet your needs. 

Is this the chemical that was the subject of the movie, “Erin Brockovich”? 
Yes. However, the maximum level detected in Santa Clara County is thousands of times lower than levels detected due to industrial contamination in Hinkley, California (the subject of the movie).

Is chromium-6 found in bottled water? 
Bottled water producers are not required to test for chromium-6. Valley Water recommends consumers contact bottled water producers directly for information about their product’s water quality. 

What is Valley Water doing about chromium-6? 
We take our responsibility to provide safe, clean water and to protect local groundwater very seriously. Valley Water and our water retailers use proven technologies and best practices to ensure drinking water delivered to residents and businesses meets or exceeds all drinking water standards. We will continue to track the science and regulations for chromium-6, and provide timely, transparent accurate information communication to our customers and the public. 


To find out more about chromium-6, please contact Geoff Tick at 408 630-2060 or [email protected].