Trivalent Versus Hexavalent Chromium: Why a Total Chromium Result Cannot Answer the Question
Many people see total chromium measurements and wonder if that number reflects the chromium-6 (hexavalent chromium) content in their water. Total chromium includes multiple chromium forms, including chromium(III) or trivalent chromium, which differs significantly in chemical properties and potential health concerns from chromium(VI). The City of Houston's public water records in Harris County show total chromium detections have a highest measured value of 6.0 micrograms per liter (µg/L) or parts per billion (ppb), while chromium-6 results range higher in some cases, with a highest value of 6.661 µg/L. This difference means total chromium data alone do not fully represent the chromium-6 levels in the water supply, so relying on total chromium may miss important details for understanding chromium-6 presence.
Why California Set Its Own 10 µg/L Limit and What That History Means for a Reader Elsewhere
California established a public health goal of 10 micrograms per liter (parts per billion) for hexavalent chromium in drinking water, motivated by scientific assessments specific to chromium-6's characteristics and potential risks. That threshold, while not a federal standard, reflects regional regulatory and health agency judgment. In Harris County’s public water system managed by the City of Houston, chromium-6 concentrations measured in federal monitoring from 2013 to 2015 ranged from just above the detection limit to a highest value of 6.661 µg/L — below California’s 10 µg/L benchmark. This suggests that chromium-6 concentrations in the local water system fall within a range that California considers for monitoring and management but have not led to federal legal limits or violations.
What the Measured Range Means Against the Relevant Federal Standard, and What It Does Not Mean
Federal regulations currently do not include a maximum contaminant level (MCL) for chromium-6 specifically. However, total chromium is regulated with an MCL of 100 micrograms per liter. The City of Houston’s public water system records show no chromium levels exceeding this total chromium MCL. It is important to understand that detecting chromium-6 above laboratory reporting limits is a measurement—not an indication of water being unsafe or in violation of any federal law. The measured results reflect the presence of chromium-6 in the source water, which comes from surface water supplies, but do not alone determine the safety or quality for individual household water without specific, personalized water testing.
The Role of Plumbing Material and Age, Separate from the Source Water
Chromium concentrations in water are influenced primarily by the water source and treatment processes rather than by household plumbing. The City of Houston water system draws from surface water, where chromium-6 presence relates to factors such as environmental sources and water chemistry. Plumbing materials and the age of home piping do not contribute chromium-6 to the water; however, they can affect other water quality parameters. Understanding your household’s plumbing condition is important for overall water quality but cannot substitute for testing the actual chromium-6 concentration in your home’s water.
How Public-System Records Differ from Private-Well Testing in What They Establish
The federal monitoring data for chromium-6 in Harris County pertain to the City of Houston's public water system, serving over 2.9 million people through nearly one million connections. These results reflect source water and system-wide treatment conditions rather than individual household water quality. Private wells, which may have very different groundwater chemistry, require specific testing to establish chromium-6 levels. If your home uses a private well or a different water provider, these public system data do not predict the exact chromium-6 content in your tap water. To make an informed treatment decision, testing your water for chromium-6 at a certified laboratory is advisable.
For households considering treatment options for chromium-6, direct-purchase Fleck Chromium-6 Filters use proven technology to address hexavalent chromium in residential water supplies. These filters ship ready to configure, providing a solution tailored for home use based on measured water quality.
In summary, government data for Harris County indicate chromium-6 is detectable in the public water system but below levels seen as cause for federal regulatory action. The distinction between total chromium and chromium-6 measurements is key to understanding these results. Plumbing materials do not affect chromium-6 levels, and private well water requires specific testing. With reliable data, households can choose appropriate treatment technologies like the Fleck Chromium-6 Filter to manage chromium(VI) in their water.
Where this information comes from
Source: EPA SDWIS public water system record. Sampled 2014-04-28. These figures describe the public water system's record, not the plumbing inside any individual building.
On record: EPA UCMR3 monitoring (2013-2015) for City of Houston (TX1010013), TX: 398 results across 2 listed contaminants, 241 detections above the reporting level; no federal MCL for hexavalent chromium; total chromium MCL 100 ug/L
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