Public water system records for the City of Houston, serving over 2.9 million people including Harris County residents, show that chromium-6 (hexavalent chromium) was detected in 178 out of 199 samples collected in the 2013-2015 EPA Unregulated Contaminant Monitoring Rule (UCMR3) survey. The highest chromium-6 measurement recorded was 6.661 micrograms per liter (µg/L), with a median detected level of 0.0985 µg/L. No federal maximum contaminant level (MCL) applies specifically to chromium-6, although total chromium has a federal MCL of 100 µg/L.
How does chromium-6 from natural sources differ from industrial contamination in water?
Chromium-6 can enter water sources through natural geogenic processes, especially in arid, alkaline aquifers, as well as from industrial activities such as metal plating and manufacturing. In Harris County, the City of Houston’s water primarily comes from surface water, which generally reflects a mix of environmental factors rather than deep aquifer geogenic sources. Understanding whether chromium-6 originates naturally or from industrial discharge helps households consider treatment needs but requires specific knowledge of local water sources and history.
Why did California establish a 10 µg/L chromium-6 limit, and what does that mean outside California?
California set its own public health goal of 10 µg/L for chromium-6, reflecting state-level risk assessments and water quality priorities. This is an advisory standard—not a federal limit—intended to guide water management and treatment decisions within that state. For residents of Harris County, Texas, where federal data show chromium-6 measurements below this level, it’s important to recognize that this California threshold does not apply federally or locally, but may serve as a useful benchmark for those weighing treatment options.
How do sample depth, well depth, or source type affect what to expect for chromium(VI) levels?
Chromium-6 concentrations can vary significantly based on whether water is sourced from shallow wells, deep aquifers, or surface water. Deeper wells may encounter different mineral profiles and geochemistry compared to surface water supplies. Since the City of Houston relies on surface water, chromium-6 levels reflect surface conditions rather than deep aquifer mineralization. In private well contexts, testing is particularly important, as local geology and well construction affect chromium-6 presence.
What does a certified laboratory test for chromium-6 include, and how should you interpret your results?
A certified lab test for chromium(VI) provides a measured concentration in micrograms per liter (µg/L), indicating the chromium-6 level present at the sample point—often the household tap or well outlet. Such testing is the only way to determine the actual chromium-6 concentration in your home’s water. Interpret results in light of federal data, local water supply types, and any applicable benchmarks or guidelines, keeping in mind that detection alone does not imply a violation or safety concern.
What was the UCMR3 survey’s purpose, and what do its findings mean for an individual household?
The EPA’s UCMR3 survey was a nationwide scientific study designed to better understand the occurrence of unregulated contaminants like chromium-6 across large water systems. Its results provide valuable context for water quality in a community but are not substitutes for home-level testing. This data cannot pinpoint individual household water quality or specific plumbing conditions, so private testing remains necessary for personalized assessment.
In summary, government records covering the City of Houston public water system serving Harris County document chromium-6 presence through a federal survey but do not establish conditions at any single household. For Harris County residents considering treatment, the Fleck Chromium-6 Filter ships ready to configure and is engineered to address chromium-6 in residential water supplies, providing a documented option for technical management of this constituent. Always begin with a certified laboratory test for your water to guide the best choice.
Source data comes from the EPA’s Safe Drinking Water Information System public water system record for City of Houston (TX1010013), available at epa.gov/dwucmr.
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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