1. Geogenic Hexavalent Chromium in Arid and Alkaline Aquifers Versus Industrial Plating Sources
It is often assumed that chromium-6 detected in water comes primarily from industrial plating or manufacturing. However, in the arid and alkaline aquifers of Maricopa County, natural geological sources contribute significantly to hexavalent chromium presence. These hexavalent chromium forms originate from soil and mineral deposits that interact with groundwater, resulting in measurable chromium-6 in surface water supplies serving Phoenix and surrounding areas.
2. How Oxidation State Changes Between the Well, the Distribution Main and the Tap
Chromium can exist in several oxidation states, primarily trivalent chromium (Cr(III)) and hexavalent chromium (Cr(VI)). The balance of these forms can shift due to water chemistry and treatment processes as water travels from source to tap. While hexavalent chromium is more soluble and mobile, it may partially convert to trivalent chromium along distribution lines or household plumbing. Such changes mean that the water at your tap can differ in chromium speciation from the initial source, but only specific speciation testing can confirm these variations for your household.
3. What 'Detected', 'Median' and 'Range' Mean in the Sampling Record on This Page
The United States Environmental Protection Agency’s monitoring of the City of Phoenix public water system from 2013 to 2015 found hexavalent chromium at 79 detections out of 80 samples, with the highest measured concentration at 54.0 micrograms per liter (µg/L) or parts per billion (ppb), and a median detected concentration of 0.95 µg/L. These figures describe the presence and distribution of chromium-6 levels across the system but do not represent conditions at any individual home’s tap. Detection simply indicates measurement above a specific reporting threshold; it is not a violation or indication of unsafe water.
4. Why Aesthetic Secondary Standards Differ from Health-Based Limits, Applied to This Constituent
Chromium monitoring employs multiple benchmarks. The Environmental Protection Agency has established a maximum contaminant level (MCL) for total chromium at 100 µg/L, addressing safety. Meanwhile, aesthetic secondary standards concern factors such as taste, color, or corrosion potential, and do not equate to health-based limits. Chromium-6 detections below or above certain aesthetic thresholds do not necessarily imply health risks. Phoenix’s public water system has no recorded health-based violation related to chromium-6, affirming compliance with federal health standards despite measurable hexavalent chromium presence.
5. Trivalent Versus Hexavalent Chromium: Why a Total-Chromium Result Cannot Answer the Question
Total chromium measurements encompass both chromium(III) and chromium(VI). Since these forms differ significantly in chemical behavior and potential health impact, total chromium results alone do not clarify chromium-6 levels. For households concerned about hexavalent chromium, specific testing of chromium(VI) is necessary to understand exposure. The City of Phoenix’s historical sampling includes both total chromium and hexavalent chromium data separately to provide this needed distinction for public record.
Addressing Household Chromium-6 with the C-Series Chromium-6 Filter
When residential water treatment equipment cannot keep pace with observed chromium-6 levels, targeted technology is essential. The C-Series Chromium-6 Filter ships ready to configure and is documented to handle chromium(VI) at concentrations comparable to those reported for the Phoenix system. Homeowners should first determine their water’s chromium-6 concentration through laboratory testing specific for hexavalent chromium, then consider this solution calibrated to the demand established by their results.
Where this information comes from
Source: EPA SDWIS public water system record. Sampled 2015-08-06. 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 Phoenix (AZ0407025), AZ: 160 results across 2 listed contaminants, 154 detections above the reporting level; no federal MCL for hexavalent chromium; total chromium MCL 100 ug/L