Opening: What is chromium-6 in my Silver Bow household water and how should I respond to equipment failure?
Chromium-6, also called hexavalent chromium or chromium(VI), is a form of chromium detected in the Butte Silver Bow public water system. When existing water treatment equipment fails, understanding local water data and treatment distinctions is key to informed household water management.
1. How ion exchange and reverse osmosis differ in what they do to chromium(VI) specifically
Ion exchange and reverse osmosis (RO) are two common water treatment technologies. Ion exchange targets dissolved ions by exchanging them with other ions on a resin, but its effectiveness for chromium(VI) depends on resin type and water chemistry. RO uses a semipermeable membrane to physically separate contaminants, including chromium(VI), from water. For chromium(VI), RO generally provides more consistent reduction by filtering out hexavalent chromium particles and dissolved ions, whereas ion exchange may vary in effectiveness depending on the system design.
2. Geogenic hexavalent chromium in arid and alkaline aquifers versus industrial plating sources
Chromium-6 in water can originate from natural geological sources or industrial activity. In arid and alkaline aquifers, chromium compounds may dissolve from rock minerals, producing geogenic hexavalent chromium. In contrast, industrial plating and manufacturing processes can introduce chromium(VI) into surface or groundwater through runoff or discharge. The Butte Silverbow Water Department’s supply is surface water serving about 33,000 people, and while chromium-6 has been detected, the source is not specified as industrial or geogenic in the sampling data.
3. Which fixtures, appliances or processes are affected first and why
Fixtures and appliances that handle significant water volume, such as kitchen sinks and ice makers, may show chromium-6 impact first due to direct water use in food preparation. Water heaters and washing machines may also be affected indirectly. Household processes involving high-volume water use present the highest opportunity for chromium-6 exposure if present. Understanding which taps channel treated water helps prioritize household attention after equipment failure.
4. How the constituent enters groundwater or the distribution system in this region
Chromium-6 enters water through natural leaching and, potentially, anthropogenic sources. In Butte Silver Bow County, sampling from 2013-2015 by the EPA found chromium-6 detected in six out of 24 samples above the reporting level of 0.03 micrograms per liter (µg/L or ppb), with a highest measured concentration of 0.0413 µg/L. The supply uses surface water, so chromium-6 presence may result from environmental factors impacting surface sources and distribution.
5. Why aesthetic secondary standards differ from health-based limits, applied to this constituent
Secondary standards for water constituents like chloride and total dissolved solids focus on taste, staining, or corrosive properties, not health risks. Chromium-6 currently has no federal maximum contaminant level (MCL) set by the EPA, although total chromium has an MCL of 100 µg/L. The Butte Silverbow Water Department’s chromium-6 measurements are well below total chromium MCLs and no health-based violations are recorded for chromium-6, underscoring the importance of distinguishing aesthetic concerns from health-based limits.
6. What 'detected', 'median' and 'range' mean in the sampling record on this page
The EPA's Unregulated Contaminant Monitoring Rule results indicate that 'detected' means the water sample contained measurable chromium-6 above the reporting level (0.03 µg/L). The 'median' of detected results (0.034 µg/L) represents the middle value of positively detected samples, while the 'range' (highest 0.0413 µg/L) shows the span of detected amounts in the sampling period. These metrics serve as an area snapshot, not an individual household water test result.
Closing: What a Silver Bow household should and should not conclude from area chromium-6 data
Residents should not assume their individual water matches public system sampling results. Only a certified laboratory test of household water can establish chromium(VI) concentration at the tap. The presence of chromium-6 detections in area water does not indicate a regulatory violation or unsafe condition by federal standards. After existing equipment failure, selecting appropriate water treatment technology—such as the Pentek Chromium-6 Filter, which ships ready to configure—can provide targeted control of chromium(VI) at the household level.
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 Butte Silverbow Water Department (MT0000170), MT: 48 results across 2 listed contaminants, 6 detections above the reporting level; no federal MCL for hexavalent chromium; total chromium MCL 100 ug/L