{"id":89054,"date":"2026-04-28T09:00:00","date_gmt":"2026-04-28T09:00:00","guid":{"rendered":"https:\/\/www.ampac1.com\/blog\/chromium-6-removal-reverse-osmosis\/"},"modified":"2026-09-29T00:42:19","modified_gmt":"2026-09-29T07:42:19","slug":"chromium-6-removal-reverse-osmosis","status":"publish","type":"post","link":"https:\/\/www.ampac1.com\/blog\/chromium-6-removal-reverse-osmosis\/","title":{"rendered":"Chromium-6 in Drinking Water: Reverse Osmosis Removal Guide"},"content":{"rendered":"<p>Chromium-6 (hexavalent chromium, Cr(VI)) became nationally known after the Hinkley, California groundwater contamination case documented in the Erin Brockovich story &#8211; but it&#8217;s a widespread contaminant, not a California-specific one. A 2016 Environmental Working Group analysis found chromium-6 in the drinking water of more than 200 million Americans across all 50 states. Reverse osmosis is one of the most effective treatment technologies available for removing chromium-6 at the point of use.<\/p>\n<h2>Chromium-6 in Drinking Water: Regulation and Health Effects<\/h2>\n<p>Chromium exists in drinking water in two primary forms with very different health profiles:<\/p>\n<ul>\n<li><strong>Chromium-3 (trivalent chromium, Cr(III)):<\/strong> An essential trace nutrient at low concentrations. EPA considers it non-carcinogenic at drinking water concentrations.<\/li>\n<li><strong>Chromium-6 (hexavalent chromium, Cr(VI)):<\/strong> A known human carcinogen. Linked to stomach and gastrointestinal cancers via ingestion. The National Toxicology Program (NTP) classified Cr(VI) as a known human carcinogen in 2024 via drinking water exposure.<\/li>\n<\/ul>\n<p>Current US regulation covers total chromium (Cr(III) + Cr(VI) combined):<\/p>\n<ul>\n<li><strong>EPA MCL for total chromium: 100 ppb (0.1 mg\/L)<\/strong> &#8211; This standard was set in 1991 and was designed primarily around Cr(III). It does not adequately protect against the carcinogenic risk of Cr(VI) at concentrations well below 100 ppb.<\/li>\n<li><strong>California MCL for Cr(VI): 10 ppb<\/strong> &#8211; California established a separate Cr(VI)-specific standard in 2014 (the first in the world), which was subsequently vacated by courts on economic feasibility grounds. California adopted a new Cr(VI) MCL of 10 ppb effective 2024.<\/li>\n<li><strong>EPA proposed federal Cr(VI) MCL:<\/strong> The EPA has been evaluating a separate, lower Cr(VI) standard for years. A federal Cr(VI)-specific MCL below 20 ppb is under active regulatory development.<\/li>\n<li><strong>Health-based guidance:<\/strong> The EPA&#8217;s non-enforceable MCLG for total chromium is 100 ppb, but public health advocates and the EWG propose a health-protective level for Cr(VI) of 0.02 ppb based on cancer risk &#8211; a standard that no practical treatment can guarantee without two-pass RO or deionization.<\/li>\n<\/ul>\n<h2>Sources of Chromium-6 in Drinking Water<\/h2>\n<ul>\n<li><strong>Natural geological sources:<\/strong> Chromium-bearing rock (chromite, serpentinite) weathering releases Cr(VI) into groundwater in many regions. California&#8217;s Central Valley, much of the Southwest, and parts of the Mountain West have naturally elevated Cr(VI) in groundwater.<\/li>\n<li><strong>Industrial contamination:<\/strong> Chromium-6 was widely used in industrial processes &#8211; chrome plating, leather tanning, cooling tower anti-corrosion additives (Pacific Gas &amp; Electric&#8217;s use of Cr(VI) in compressor station cooling towers is the Hinkley case), and aerospace manufacturing. Decades of industrial use left Cr(VI) in groundwater near thousands of industrial sites.<\/li>\n<li><strong>Coal ash leachate:<\/strong> Coal combustion residuals (fly ash) contain chromium; coal ash impoundments near power plants are a documented source of Cr(VI) in nearby groundwater.<\/li>\n<\/ul>\n<h2>How Reverse Osmosis Removes Chromium-6<\/h2>\n<p>Chromium-6 exists in water as chromate (CrO\u2084\u00b2\u207b) and dichromate (Cr\u2082O\u2087\u00b2\u207b) &#8211; both are highly soluble anions. RO membranes reject chromate through charge repulsion (divalent anion) and size exclusion:<\/p>\n<table class=\"table table-bordered\">\n<thead>\n<tr>\n<th>Chromium Species<\/th>\n<th>Charge<\/th>\n<th>Typical RO Rejection<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Chromate (CrO\u2084\u00b2\u207b) &#8211; Cr(VI) at neutral\/alkaline pH<\/td>\n<td>Divalent anion<\/td>\n<td>92-97%<\/td>\n<\/tr>\n<tr>\n<td>Dichromate (Cr\u2082O\u2087\u00b2\u207b) &#8211; Cr(VI) at acidic pH<\/td>\n<td>Divalent anion<\/td>\n<td>92-97%<\/td>\n<\/tr>\n<tr>\n<td>Chromium(III) (Cr\u00b3\u207a) &#8211; Cr(III) at acidic to neutral pH<\/td>\n<td>Trivalent cation<\/td>\n<td>96-99%<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p>Practical example: Feed water at 50 ppb Cr(VI) through a well-maintained TFC RO system at proper operating conditions (50 PSI minimum, 77\u00b0F, 15% recovery or less for point-of-use) will typically produce permeate at 1.5-4 ppb Cr(VI) &#8211; well below California&#8217;s 10 ppb MCL and significantly below the federal 100 ppb MCL.<\/p>\n<p><strong>NSF P473 and chromium:<\/strong> NSF Protocol P473 is a certification standard for drinking water treatment units for PFAS reduction that also evaluates chromium-6. Some RO systems tested under NSF P473 show Cr(VI) rejection achieving 95%+ under standardized test conditions. Look for NSF P473 certification when selecting a system for chromium-6 reduction.<\/p>\n<h2>Chromium-6 Treatment Options Compared<\/h2>\n<table class=\"table table-bordered\">\n<thead>\n<tr>\n<th>Technology<\/th>\n<th>Cr(VI) Removal<\/th>\n<th>Notes<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Reverse osmosis<\/td>\n<td>92-97%<\/td>\n<td>Most versatile. Removes Cr(VI) plus TDS, PFAS, nitrates, arsenic, lead. Point-of-use and whole-house options.<\/td>\n<\/tr>\n<tr>\n<td>Anion exchange resin (Cr(VI)-selective)<\/td>\n<td>95-99%<\/td>\n<td>High Cr(VI) removal. Regeneration produces chromium-laden brine requiring proper disposal. Higher maintenance than RO.<\/td>\n<\/tr>\n<tr>\n<td>Reduction + filtration (Fe\u00b2\u207a or SO\u2082 reduction to Cr(III), then filtration)<\/td>\n<td>90-99%<\/td>\n<td>Municipal-scale treatment. Converts Cr(VI) to Cr(III) then precipitates. Not practical at residential scale.<\/td>\n<\/tr>\n<tr>\n<td>Activated carbon<\/td>\n<td>&lt;10%<\/td>\n<td>Standard activated carbon does NOT remove Cr(VI). A common misconception.<\/td>\n<\/tr>\n<tr>\n<td>Water softener<\/td>\n<td>&lt;10%<\/td>\n<td>Does NOT remove Cr(VI). Softeners are designed for cation removal; chromate is an anion.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<h2>Testing for Chromium-6<\/h2>\n<p>Standard water tests for &#8220;total chromium&#8221; do not distinguish Cr(VI) from Cr(III). If you&#8217;re concerned about chromium-6 specifically &#8211; particularly if you&#8217;re in California, near industrial sites, or in a region with naturally elevated chromium &#8211; request a test that specifies Cr(VI) (hexavalent chromium) separately from total chromium.<\/p>\n<p>Municipal water users: Your utility&#8217;s annual Consumer Confidence Report (CCR) reports total chromium. For Cr(VI) specifically, contact your utility directly &#8211; California utilities subject to the 10 ppb MCL must test and report Cr(VI) separately. For private well users, a state-certified laboratory test for Cr(VI) typically costs $25-60.<\/p>\n<h2>AMPAC USA RO Systems for Chromium-6 Reduction<\/h2>\n<p>AMPAC USA residential reverse osmosis systems using FILMTEC\u2122 thin-film composite membranes achieve 92-97% rejection of chromate (Cr(VI)) under standard operating conditions. For households with chromium-6 in drinking water:<\/p>\n<ul>\n<li><strong>Under-sink (50-100 GPD)<\/strong> &#8211; Treats drinking and cooking water. Appropriate for most households where the primary concern is ingestion exposure from the drinking tap.<\/li>\n<li><strong>Whole-house (200-1,000+ GPD)<\/strong> &#8211; Full-home treatment including shower and bath water. While Cr(VI) absorption through skin contact is considered lower risk than ingestion, whole-house RO is recommended for facilities with high Cr(VI) concentrations or where comprehensive exposure reduction is desired.<\/li>\n<\/ul>\n<p><strong>Water test showing elevated chromium-6?<\/strong> Share your results &#8211; including Cr(VI) concentration, pH, and TDS &#8211; and we&#8217;ll specify the right system. <a href=\"\/\">Contact AMPAC USA<\/a> for a free consultation. One business day response.<\/p>\n<p><em>Related: <a href=\"\/blog\/reverse-osmosis-pfas-removal\/\">PFAS Removal by Reverse Osmosis<\/a> | <a href=\"\/blog\/arsenic-removal-reverse-osmosis\/\">Arsenic Removal by Reverse Osmosis<\/a> | <a href=\"\/blog\/lead-removal-reverse-osmosis\/\">Lead Removal by Reverse Osmosis<\/a> | <a href=\"https:\/\/www.ampac1.com\/products\">Residential RO Systems<\/a><\/em><\/p>\n<h2>Related Articles<\/h2>\n<ul>\n<li><a href=\"https:\/\/www.ampac1.com\/blog\/nitrate-removal-reverse-osmosis\/\">Nitrate Removal by Reverse Osmosis: Well Water Treatment Guide | AMPAC USA<\/a><\/li>\n<li><a href=\"https:\/\/www.ampac1.com\/blog\/lead-removal-reverse-osmosis\/\">Lead in Drinking Water: How Reverse Osmosis Removes Lead | AMPAC USA<\/a><\/li>\n<li><a href=\"https:\/\/www.ampac1.com\/blog\/iron-removal-reverse-osmosis\/\">Iron in Well Water: Does Reverse Osmosis Remove Iron? | AMPAC USA<\/a><\/li>\n<li><a href=\"https:\/\/www.ampac1.com\/blog\/fluoride-removal-reverse-osmosis\/\">Fluoride Removal by Reverse Osmosis: Does RO Filter Fluoride? | AMPAC USA<\/a><\/li>\n<\/ul>\n<h2>Frequently Asked Questions<\/h2>\n<p><strong>Does reverse osmosis remove chromium-6 from drinking water?<\/strong><br \/>Yes. RO rejects chromate (Cr(VI)) at 92-97 percent through charge repulsion and size exclusion, since chromate is a divalent anion. Feed water at 50 ppb Cr(VI) typically produces permeate at 1.5-4 ppb, well below California&#8217;s 10 ppb standard.<\/p>\n<p><strong>Does activated carbon or a water softener remove chromium-6?<\/strong><br \/>No. Standard activated carbon removes less than 10 percent of chromium-6, and water softeners are designed for cation removal while chromate is an anion, so neither is an effective standalone treatment.<\/p>\n<p><strong>What&#8217;s the difference between chromium-3 and chromium-6 in drinking water?<\/strong><br \/>Chromium-3 is an essential trace nutrient considered non-carcinogenic at drinking water concentrations, while chromium-6 is a known human carcinogen linked to stomach and gastrointestinal cancers. Current EPA regulation only covers total chromium at 100 ppb, which does not adequately address chromium-6 risk at lower concentrations.<\/p>\n<p><strong>How do I know if my water has chromium-6 specifically?<\/strong><br \/>Standard total chromium tests don&#8217;t distinguish Cr(VI) from Cr(III). You need to request a test that specifically reports hexavalent chromium separately, especially if you&#8217;re in California, near industrial sites, or in a region with naturally elevated chromium.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Chromium-6 (hexavalent chromium, Cr(VI)) became nationally known after the Hinkley, California groundwater contamination case documented in the Erin Brockovich story&#8230;<\/p>\n","protected":false},"author":1,"featured_media":89085,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"site-sidebar-layout":"default","site-content-layout":"","ast-site-content-layout":"default","site-content-style":"default","site-sidebar-style":"default","ast-global-header-display":"","ast-banner-title-visibility":"","ast-main-header-display":"","ast-hfb-above-header-display":"","ast-hfb-below-header-display":"","ast-hfb-mobile-header-display":"","site-post-title":"","ast-breadcrumbs-content":"","ast-featured-img":"","footer-sml-layout":"","ast-disable-related-posts":"","theme-transparent-header-meta":"","adv-header-id-meta":"","stick-header-meta":"","header-above-stick-meta":"","header-main-stick-meta":"","header-below-stick-meta":"","astra-migrate-meta-layouts":"default","ast-page-background-enabled":"default","ast-page-background-meta":{"desktop":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"tablet":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"mobile":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""}},"ast-content-background-meta":{"desktop":{"background-color":"var(--ast-global-color-4)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"tablet":{"background-color":"var(--ast-global-color-4)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"mobile":{"background-color":"var(--ast-global-color-4)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""}},"footnotes":""},"categories":[493,491],"tags":[],"class_list":["post-89054","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-drinking-water","category-water-purification"],"_links":{"self":[{"href":"https:\/\/www.ampac1.com\/blog\/wp-json\/wp\/v2\/posts\/89054","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.ampac1.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.ampac1.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.ampac1.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.ampac1.com\/blog\/wp-json\/wp\/v2\/comments?post=89054"}],"version-history":[{"count":0,"href":"https:\/\/www.ampac1.com\/blog\/wp-json\/wp\/v2\/posts\/89054\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.ampac1.com\/blog\/wp-json\/wp\/v2\/media\/89085"}],"wp:attachment":[{"href":"https:\/\/www.ampac1.com\/blog\/wp-json\/wp\/v2\/media?parent=89054"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.ampac1.com\/blog\/wp-json\/wp\/v2\/categories?post=89054"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.ampac1.com\/blog\/wp-json\/wp\/v2\/tags?post=89054"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}