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Understanding the Local Aquifer and Water Supply in Tucson, Pima County

The Tucson metropolitan area in Pima County relies heavily on groundwater drawn from deep aquifers. These waters are sourced from natural geological formations and then distributed through a regulated public water system known as Metropolitan DWID (AZ0410076). This community water system serves over 45,000 people, delivering water through more than 18,000 connections. Water quality monitoring follows stringent protocols to ensure compliance with federal and state guidelines.

Myth 1: A Total Chromium Test Fully Describes Chromium-6 Concerns

It is often assumed that measuring total chromium in water suffices to understand chromium-6 (hexavalent chromium) presence. However, total chromium combines all oxidation states, including trivalent chromium (chromium-3), which behaves very differently chemically and biologically. Hexavalent chromium, or chromium(VI), is a specific form detected separately during monitoring. The Metropolitan DWID system's testing from 2013 to 2015 shows distinct chromium-6 results with 88 samples taken, 87 detecting chromium(VI) above the minimal reporting threshold of 0.03 micrograms per liter (µg/L or ppb). The highest measured chromium-6 was 3.0 µg/L, with a median at 0.16 µg/L. Total chromium results reflect separate values, with a maximum of 1.7 µg/L in those samples. This distinction matters when considering treatment approaches tailored for chromium(VI).

Myth 2: Ion Exchange and Reverse Osmosis Work the Same Way to Address Chromium-6

Homeowners weighing treatment methods should note that ion exchange and reverse osmosis technologies differ significantly in their operational principles and effectiveness on chromium(VI). Ion exchange involves exchanging ions in water with ions on a resin medium, which can be selective for chromium-6 species depending on the resin used. Reverse osmosis, on the other hand, relies on a membrane barrier that physically separates dissolved substances, including chromium(VI), from water, often reducing more constituents but with different water waste considerations. Selecting between these depends on your household needs, water chemistry, and maintenance preferences.

Myth 3: A Certified Water Test Report Will Tell You Exactly What Chromium-6 Level You Have Without Additional Context

Certified laboratory reports for chromium-6 provide concentration values typically in micrograms per liter or parts per billion. These reports identify only the sample tested, which may vary within a region or distribution system. The government’s Metropolitan DWID record offers a broader statistical context but does not describe individual household water. Therefore, testing your own water through a certified lab is essential for precise knowledge. Reading such reports requires understanding detection limits and the difference between median values and maximum detected concentrations in the regional record.

Myth 4: Chromium-6 Levels in Tucson’s Water Are Stable Throughout the Year

Chromium-6 concentrations can vary seasonally or across years due to natural aquifer dynamics, groundwater recharge conditions, and system operations. The Metropolitan DWID dataset covers samples taken over about a year from August 2014 to August 2015. Variability exists between individual sample results, with values ranging from just above 0.03 µg/L up to 3.0 µg/L. Awareness of potential fluctuations helps homeowners understand that a single test may not represent long-term exposure, highlighting the value of regular monitoring.

Myth 5: Interpreting the Median and Range from Regional Data Applies Directly to Every Home

The median chromium-6 concentration found in the Metropolitan DWID system was 0.16 µg/L, meaning half the measurements were below and half above this value during the study period. The range extends up to 3.0 µg/L, reflecting the highest measurements recorded. While this summary informs general water quality trends, individual household water may be higher or lower depending on plumbing and local conditions. Understanding this range aids in evaluating potential treatment benefits and in deciding if specialized equipment is warranted.

Conclusion: Scope and Source of Tucson’s Chromium-6 Data

The information outlined comes strictly from the EPA public water system record for Metropolitan DWID, covering water sourced from Tucson’s groundwater aquifer serving over 45,000 residents. This record does not indicate any health-based violations related to chromium-6 or other contaminants. For precise assessment, testing your household water through a certified laboratory is recommended. Technologies such as the Fleck Chromium-6 Filter ship ready to configure and offer technical solutions tailored to chromium(VI) concerns. You can consult the EPA’s official database for the full Metropolitan DWID water quality report to inform further decisions.

Where this information comes from

Source: EPA SDWIS public water system record. Sampled 2015-08-31. These figures describe the public water system's record, not the plumbing inside any individual building.

On record: EPA UCMR3 monitoring (2013-2015) for Metropolitan DWID (AZ0410076), AZ: 176 results across 2 listed contaminants, 165 detections above the reporting level; no federal MCL for hexavalent chromium; total chromium MCL 100 ug/L