Water supplied by Memphis Light, Gas & Water in Shelby County originates from groundwater sources, serving a population of approximately 659,500 people. The water reaches residential taps after treatment and distribution through an extensive network of over 255,000 connections.
Trivalent Versus Hexavalent Chromium: Why Total Chromium Results Aren’t Enough
Chromium occurs in several forms in water, primarily trivalent chromium (Cr(III)) and hexavalent chromium (chromium-6 or Cr(VI)). While total chromium measurements aggregate all forms, understanding chromium-6 specifically matters due to its different chemical behavior. The EPA data for Memphis’s public water system from 2013 to 2015 reported no detections above the reporting level for total chromium. However, for chromium-6, detections occurred in 7 out of 40 samples, with levels up to 0.1 micrograms per liter (µg/L) or parts per billion (ppb). These figures represent measurements above the reporting threshold, not violations or unsafe levels.
How Ion Exchange and Reverse Osmosis Differ in Addressing Chromium(VI)
When considering treatment options for hexavalent chromium in residential water, two main technologies offer distinct approaches. Ion exchange involves exchanging chromium-6 ions in the water with other ions using a resin medium. Reverse osmosis forces water through a semi-permeable membrane, physically separating contaminants including chromium-6. Each method targets chromium-6 specifically and can be effective depending on water chemistry and household needs.
The Role of Plumbing Material and Age, Separate from the Source Water
Chromium-6 levels in tap water are influenced mainly by the source water and treatment process, but plumbing materials and the age of household pipes also play a role. Unlike metals like lead or copper, chromium-6 does not commonly leach from plumbing materials. Therefore, detected chromium-6 concentrations relate primarily to the groundwater supply and water system treatment rather than in-home plumbing.
How Many Samples and Wells Stand Behind the Figures, and What a Small Sample Means
The EPA Unregulated Contaminant Monitoring Rule (UCMR3) data reflects 40 water samples collected between 2013 and 2015 for the Memphis Light, Gas & Water system. These samples represent a snapshot of system-wide water quality rather than individual household conditions. A relatively small number of samples means variations can occur, and the data should be considered system-level evidence rather than specific to any one well or home.
What Happens When This Problem is Left Untreated for Years, Stated Without Exaggeration
While the Memphis water system has no health-based violations on record, long-term consumption of hexavalent chromium at elevated levels has raised concerns in various studies. Hexavalent chromium is chemically more reactive than trivalent chromium and may affect water taste or cause staining. The EPA currently has no federal maximum contaminant level set for chromium-6, though total chromium is regulated with a limit far above the detected chromium-6 levels here.
What a Certified Laboratory Test for This Constituent Reports and How to Read It
To know the chromium-6 concentration in your household water, an individual water sample sent to a certified laboratory is necessary. The report will specify chromium-6 levels in micrograms per liter (µg/L or ppb). Comparing these results with local government sampling can provide context, but only direct testing of your water can establish your specific chromium-6 concentration.
What Not to Conclude From Area Data
The EPA data for the Memphis Light, Gas & Water system does not indicate violations or unsafe conditions regarding chromium-6. Detecting chromium-6 at levels below health-based legal limits in some system samples does not mean individual homes have the same levels or face health risks. To address any concerns, testing your household water is essential. For those seeking treatment, the Pentek Chromium-6 Filter ships ready to configure and uses proven technology to specifically address chromium-6 in residential water.
Where this information comes from
Source: EPA SDWIS public water system record. Sampled 2015-12-08. These figures describe the public water system's record, not the plumbing inside any individual building.
On record: EPA UCMR3 monitoring (2013-2015) for Memphis Light, Gas & Water (TN0000450), TN: 80 results across 2 listed contaminants, 7 detections above the reporting level; no federal MCL for hexavalent chromium; total chromium MCL 100 ug/L
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