Oxidation State Changes of Chromium from Source to Tap
Hexavalent chromium is chromium in its +6 oxidation state (Cr(VI))
This form, also known as chromium-6 or chromium(VI), is chemically distinct from trivalent chromium (Cr(III)) and can behave differently in water chemistry. Surface water sourced by San Antonio Water System and distributed in Bexar County may carry chromium primarily as chromium-6, depending on environmental and treatment conditions.
Distribution system conditions alter chromium's chemical forms
Between the water source and household taps, changes in pH, oxidation-reduction potential, and contact with pipe materials can influence chromium speciation, sometimes converting hexavalent chromium to other forms or vice versa. This dynamic impacts what a laboratory measures in a sample taken directly from the tap.
Laboratory reports reflect chromium-6 present at the tap, not solely at the source
Results represent chromium(VI) concentrations after water travels through the distribution mains and household plumbing, combining all chemical and physical changes up to the sampling point.
Sources of Hexavalent Chromium in Bexar County Water
Geogenic contributions linked to natural aquifer conditions
Some chromium-6 arises naturally in groundwater in regions characterized by arid, alkaline conditions, although Bexar County's system primarily uses surface water. Natural levels can vary with geological formations and environmental factors.
Anthropogenic influences from industrial activities may contribute
Industrial processes such as metal plating and manufacturing can release chromium-6 into water supplies, but municipal treatment and source water control aim to manage these inputs effectively for public water systems like San Antonio Water System.
Public water system monitoring captures combined effects
The EPA's Unregulated Contaminant Monitoring Rule (UCMR3) data reflect a composite of all influencing factors in the public system serving Bexar County residents.
Interpreting Certified Laboratory Testing for Chromium-6
Samples report chromium-6 concentrations in micrograms per liter (µg/L) or parts per billion (ppb)
These units are equivalent and indicate the mass of chromium-6 per volume of water tested. Reporting levels set detection thresholds at 0.03 µg/L, meaning values below this may not be quantified.
Detection indicates measurable presence, not a regulatory violation
Though chromium-6 was detected in 136 of 145 samples for Bexar County's public water system, with a highest recorded value of 1.8 µg/L, no federal maximum contaminant level (MCL) exists specifically for hexavalent chromium. The total chromium MCL remains at 100 µg/L.
Test results do not reflect individual household water conditions
Only direct testing of a specific home's water supply can reveal its actual chromium-6 concentration, given variations in plumbing, fixtures, and sampling protocols.
Reading the Record's Median and Range for Household Interpretation
The median chromium-6 detection in the system was 0.096 µg/L
This means half the detected values were below and half above this point within the recorded sample set from 2013 to 2015.
The range of chromium-6 detections spanned from just above 0.03 µg/L to 1.8 µg/L
This spread shows variability in concentrations measured across the system's service area, indicating that chromium-6 levels vary spatially and temporally.
Chromium total measurements offer a broader elemental perspective
Total chromium detections ranged from 0.2 µg/L to a maximum of 6.3 µg/L with a median at 0.26 µg/L, well under the established total chromium MCL of 100 µg/L.
Comparing Bexar County’s Chromium-6 Data with Neighboring Areas
Use federal monitoring records for adjacent counties cautiously
Each public water system's sampling reflects conditions specific to its source water and treatment practices, so statistical ranges cannot be directly mapped from one to another without considering environmental and operational differences.
Similar detection patterns may arise in regions with comparable water sources
Surface water systems in Texas often share detection characteristics due to regional geology and land use but site-specific testing is necessary for household decisions.
Avoid assuming comparable household levels based on area-wide data
Individual household water quality depends on plumbing and local distribution conditions, so test-based decisions should rely on in-home sampling.
For residential situations in Bexar County where chromium-6 is a consideration, evaluating technical approaches to address chromium-6 concentrations typically follows testing at the home to identify demand. The Pentair Chromium-6 Filter ships ready to configure and offers targeted treatment addressing measured levels of hexavalent chromium focused on household water needs.
Where this information comes from
Source: EPA SDWIS public water system record. Sampled 2015-12-04. These figures describe the public water system's record, not the plumbing inside any individual building.
On record: EPA UCMR3 monitoring (2013-2015) for San Antonio Water System (TX0150018), TX: 290 results across 2 listed contaminants, 229 detections above the reporting level; no federal MCL for hexavalent chromium; total chromium MCL 100 ug/L
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