Trivalent Versus Hexavalent Chromium: Why Total Chromium Results Don’t Tell the Full Story
A frequent misconception is that measuring total chromium alone fully explains the chromium content in your water. Total chromium includes several chemical forms, notably trivalent chromium and hexavalent chromium (chromium-6 or chromium(VI)). These species differ significantly in properties and concerns. Government data for the Des Moines Waterworks system show monitoring for both total chromium and chromium-6 separately, reflecting this difference. Total chromium includes chromium(III), which is nutritionally essential at trace levels, whereas chromium(VI) is considered separately due to its distinct behavior in water.
Differences in How Ion Exchange and Reverse Osmosis Address Chromium(VI)
When existing treatment equipment fails, selecting the right technology to manage chromium-6 in household water becomes crucial. Ion exchange technologies specifically target chromium(VI) ions, exchanging them for other non-harmful ions, and can be effective in reducing chromium-6 concentrations. Reverse osmosis (RO) membranes physically filter dissolved substances including chromium(VI), but performance may vary based on membrane quality and operating conditions. Understanding these differences helps in deciding what equipment to put in place that ships ready to configure after your prior equipment has ceased functioning properly.
Reading Certified Laboratory Reports on Chromium-6 Levels
For precise information about chromium-6 in your household water, a certified laboratory test is essential. Such tests commonly express chromium-6 concentration in micrograms per liter (µg/L), which equals parts per billion (ppb). The EPA’s 2013–2015 unregulated contaminant monitoring rule (UCMR3) results for Des Moines Waterworks noted chromium-6 detections ranging up to 2.62 µg/L, with a median of about 0.2235 µg/L among detections. These figures come from system-wide monitoring and are not specific to any one home, so your individual water test could be different. Interpreting these results helps you understand your exposure relative to local water system data.
Why Aesthetic Secondary Standards Differ from Health-Based Limits for Chromium-6
It is important to distinguish between secondary standards, which relate to taste, staining, and plumbing effects, and health-based limits set by regulatory agencies. For chromium-6, there is no federal maximum contaminant level (MCL) specifically established yet. The total chromium MCL is 100 µg/L. The EPA data for Des Moines Waterworks show no federal health-based violations for chromium-6. This means the presence of chromium-6 detected in the water system is not classified as unsafe by federal standards but may impact water aesthetics or corrosion characteristics. Recognizing this distinction helps in evaluating the necessity and urgency of treatment equipment replacement.
How Chromium-6 Enters Groundwater or the Distribution System in Polk County
In Des Moines, the water source is surface water rather than groundwater. Chromium-6 can enter surface water through natural mineral deposits or from industrial sources upstream. Seasonal and other environmental factors can influence concentrations, but the system-wide monitoring data provide a snapshot of typical ranges. Distribution system materials and water treatment steps before delivery also affect chromium-6 levels. Understanding these entry points clarifies how chromium-6 appears in your home's tap water and why it requires targeted treatment after existing equipment failure.
The Role of Plumbing Materials and Age, Separate from Source Water
Your home's plumbing materials and the age of pipes can influence water quality independently from what is found in the source water. Older plumbing components may interact with water chemistry, sometimes altering metal concentrations or water corrosivity. However, chromium-6 presence originates mainly from the water supply rather than household plumbing. Identifying this difference ensures focus on both water supply testing and plumbing evaluation when assessing chromium-6 levels and deciding on a treatment approach.
Next Steps: Ordering the Right Test to Clarify Your Household Chromium-6 Level
To resolve uncertainty about chromium-6 after your previous equipment has failed, order a certified laboratory test specifically reporting hexadecimal chromium (chromium-6 or chromium(VI)) concentration in micrograms per liter (µg/L). A clear result will inform whether treatment with a Fleck Chromium-6 Filter, which ships ready to configure and specializes in chromium(VI) management, is appropriate for your household. This test is the definitive step needed to understand your water and decide on necessary treatment for peace of mind in Polk County.
Where this information comes from
Source: EPA SDWIS public water system record. Sampled 2015-04-01. These figures describe the public water system's record, not the plumbing inside any individual building.
On record: EPA UCMR3 monitoring (2013-2015) for Des Moines Waterworks (IA7727031), IA: 48 results across 2 listed contaminants, 32 detections above the reporting level; no federal MCL for hexavalent chromium; total chromium MCL 100 ug/L