What Is Cadmium?
Cadmium is a soft, bluish-white heavy metal that occurs naturally in the earth’s crust, almost always bound together with zinc, lead, and copper ores rather than existing on its own. Industrially, it has been used for decades in rechargeable nickel-cadmium (NiCd) batteries, metal plating and coating, pigments for plastics and paints, and as a stabilizer in some PVC products. None of that industrial usefulness translates into safety once cadmium ends up in drinking water.
Unlike calcium or magnesium, cadmium serves no biological function in the human body — there is no dose at which it is beneficial, and the body has no efficient mechanism for excreting it once absorbed. It accumulates in tissue over a lifetime, with a biological half-life in the kidneys measured in decades rather than days. The International Agency for Research on Cancer (IARC) classifies cadmium and cadmium compounds as a Group 1 carcinogen — the same category as asbestos and benzene — though that classification is driven primarily by occupational inhalation exposure (welding fumes, battery manufacturing, smelting) rather than by drinking water.
Cadmium is colorless, odorless, and tasteless in water at the concentrations that matter for health, so there is no sensory way to detect it. You cannot smell, taste, or see a cadmium problem in your tap water — the only way to know is through utility monitoring data or a laboratory test.
The contaminant’s most infamous case study is itai-itai disease (“ouch-ouch disease”), documented in Japan’s Toyama Prefecture starting in the 1910s, where decades of cadmium-contaminated irrigation water from an upstream zinc mine caused severe bone demineralization and kidney failure in local rice farmers. It remains the clearest historical demonstration of what sustained, high-dose cadmium exposure through water and food can do to the human skeleton and kidneys — and it is why cadmium’s drinking water standard, unlike some heavy metals, is built around a specific, measurable organ-damage threshold rather than a theoretical cancer risk.
How Cadmium Gets Into Drinking Water
Cadmium reaches drinking water through two distinct pathways: environmental contamination of the water source, and corrosion of household and utility plumbing materials on the way to the tap. In the United States, the plumbing pathway is by far the more common reason a specific household sees elevated cadmium, even in cities where the raw source water is clean.
Galvanized Pipe and Plumbing Corrosion
Cadmium is a common trace impurity in the zinc coating used to galvanize steel pipe — the “galvanization” process that made galvanized steel a standard water-supply material for much of the 20th century, particularly in homes built before the 1960s. As galvanized pipe ages and its zinc coating corrodes, that coating releases not just zinc but the cadmium impurities trapped within it, directly into the water flowing through the pipe. This is functionally the same story as lead leaching from lead service lines or copper leaching from copper pipe: the metal isn’t in the source water, it’s in the infrastructure delivering it.
Cadmium can also leach from certain low-quality plumbing solders, fittings, and faucet components, and from some older galvanized well casings and pressure tanks in rural water systems. As with lead and copper, water that sits stagnant in galvanized plumbing overnight or during periods of non-use accumulates the highest cadmium concentrations, and first-draw tap water — the water sitting in the pipe closest to the faucet — typically carries the most.
Industrial and Agricultural Sources
Beyond plumbing, cadmium enters source water from discharge from metal refineries and electroplating operations, where cadmium is a byproduct of zinc, lead, and copper smelting. Runoff from improperly disposed batteries — particularly older nickel-cadmium rechargeable batteries — and from waste paint pigments can carry cadmium into surface water and groundwater near landfills and industrial sites. Phosphate fertilizers used in commercial agriculture often contain cadmium as a natural impurity from the phosphate rock they’re derived from; over decades of application, this can elevate cadmium levels in agricultural runoff and in groundwater beneath heavily fertilized cropland.
Geographic Hotspots
Cadmium contamination in US drinking water source is not evenly distributed. Areas with a legacy of zinc, lead, or copper mining and smelting — parts of the Rocky Mountain West, the Tri-State Mining District spanning Missouri, Kansas, and Oklahoma, and portions of the Midwest with historic industrial metal-processing activity — see the highest rates of source-water cadmium detections. Separately, any community with a large stock of pre-1960s housing that still relies on original galvanized supply lines carries elevated plumbing-related risk regardless of geography.
Health Effects
Cadmium’s defining chronic health effect is kidney damage — specifically injury to the renal tubules, the structures responsible for reabsorbing nutrients and filtering waste from blood. This kidney effect, not cancer, is what EPA’s drinking water standard is built around, because it occurs at lower, more directly measurable doses than cancer risk from ingestion.
Kidney (Renal Tubular) Damage
Chronic low-level cadmium exposure accumulates in the kidneys over years to decades, progressively impairing the renal tubules’ ability to reabsorb proteins, glucose, and calcium. Early-stage cadmium-related kidney damage is typically detected as low-molecular-weight proteinuria — small proteins leaking into urine that shouldn’t be there — well before any symptoms are noticeable. Left unaddressed over a long enough exposure period, this tubular damage can progress toward reduced kidney function and, in severe historical cases like itai-itai disease, contribute to broader systemic failure. Because the kidney effect is threshold-based — meaning damage becomes significant only above a certain sustained exposure level — the EPA’s drinking water limit is set specifically to keep lifetime exposure below that threshold.
Bone Effects
Cadmium interferes with the body’s calcium metabolism and vitamin D activation, which over long-term high exposure can lead to bone demineralization, increased fracture risk, and osteoporosis-like effects. This was the most visually severe manifestation in the itai-itai disease cases in Japan, where decades of cadmium exposure through contaminated rice and irrigation water caused extremely painful bone deformities and fractures in affected residents, disproportionately among women who had gone through multiple pregnancies. That historical episode remains the clearest evidence of what sustained, high-dose environmental cadmium exposure can do to the human skeleton, and it’s the benchmark toxicologists still reference when modeling cadmium’s dose-response relationship.
Cancer Risk
IARC classifies cadmium and cadmium compounds as Group 1 — carcinogenic to humans — based primarily on strong evidence linking occupational cadmium exposure, largely through inhalation of cadmium dust and fumes in battery manufacturing, welding, and smelting, to lung cancer. The evidence for cancer risk from cadmium in drinking water specifically is considerably weaker than the inhalation evidence, which is why EPA’s drinking water standard is grounded in the kidney (non-cancer) endpoint rather than a cancer slope factor. The Group 1 classification is still meaningful context — it reflects cadmium’s overall toxicological profile — but it should not be read as implying drinking-water cadmium carries the same cancer risk as occupational inhalation exposure.
Children
Children absorb a higher proportion of ingested cadmium than adults — up to five times more efficiently in some studies — partly because children are more likely to be iron-deficient, and iron deficiency increases the body’s cadmium absorption rate through shared metabolic pathways. Because cadmium accumulates over a lifetime with minimal excretion, exposure that begins in childhood contributes to a larger cumulative body burden by adulthood than exposure starting later in life.
Pregnant Women
Cadmium crosses the placenta to a limited degree, and it accumulates in placental tissue itself, where it can interfere with the transfer of essential nutrients like zinc and calcium to the developing fetus. Some studies have linked elevated maternal cadmium levels to lower birth weight. Pregnant women in homes with older galvanized plumbing or private wells in industrial or agricultural areas should be particularly attentive to testing their water.
EPA Regulation and Limits
The EPA set cadmium’s Maximum Contaminant Level (MCL) at 0.005 mg/L (5 parts per billion, or 5 ppb), and — unlike many regulated contaminants where the health-based goal (MCLG) is set at zero — cadmium’s Maximum Contaminant Level Goal is also 0.005 mg/L, the identical figure. This reflects the threshold-based nature of cadmium’s key health endpoint: unlike a non-threshold carcinogen where theoretically no exposure level is fully “safe,” kidney damage from cadmium requires sustained exposure above a specific dose to occur, so EPA calculated the highest level at which no adverse renal effects are expected over a lifetime of exposure and set both numbers there.
| Standard | Value | Notes |
|---|---|---|
| EPA MCL (enforceable limit) | 0.005 mg/L (5 ppb) | Legally enforceable at public water systems |
| EPA MCLG (health goal) | 0.005 mg/L (5 ppb) | Same as MCL — threshold-based on kidney (renal tubular) damage |
| WHO guideline value | 0.003 mg/L (3 ppb) | Stricter than the US MCL |
| IARC classification | Group 1 | Carcinogenic to humans — primarily occupational inhalation evidence |
| Monitoring frequency | Varies by system size and history | Public systems test on a regulatory schedule under SDWIS |
The gap between the US standard (5 ppb) and the WHO guideline (3 ppb) is worth noting for context, though it does not mean US tap water at 4 ppb cadmium is “unsafe” by international standards in any binding sense — WHO guidelines are recommendations, not enforceable limits, and reflect a different risk-management approach than EPA’s statutory framework. There is currently no pending EPA rulemaking specifically targeting a revision to the cadmium MCL; regulatory attention to metals in drinking water in recent years has been concentrated on lead and PFAS.
How Widespread Is Cadmium?
Cadmium MCL exceedances at public water systems are uncommon nationally. The vast majority of US community water systems report cadmium levels well under the 5 ppb limit in routine SDWIS compliance monitoring, and cadmium rarely appears as a driver of enforcement actions the way lead, nitrate, or disinfection byproducts do.
Where cadmium problems do occur, they concentrate in a few identifiable situations rather than appearing as a diffuse national risk. Homes and small systems with original pre-1960s galvanized plumbing are the most common source of elevated household-level cadmium, independent of what the municipal source water looks like — this mirrors the household-plumbing pattern seen with copper. Private wells in areas with a history of zinc, lead, or copper mining, smelting, or heavy phosphate fertilizer use carry elevated risk, and because private wells are not covered by EPA’s public water system regulations, well owners are responsible for testing on their own. Small water systems located near current or former metal-processing facilities occasionally show source-water cadmium levels that require closer monitoring or treatment.
Because the plumbing pathway dominates household-level exposure, utility-reported compliance data for a city does not necessarily reflect what comes out of an individual tap — a pattern also seen with lead and copper, where the water leaving the treatment plant can be clean while water sitting in an old service line or galvanized branch line picks up metal before reaching the faucet.
How WaterVerge Tracks Cadmium
WaterVerge sources cadmium monitoring data from the EPA’s Safe Drinking Water Information System (SDWIS), which contains the compliance sampling results public water systems are required to report under the Safe Drinking Water Act. For each system, WaterVerge displays the most recent reported cadmium concentration alongside the 5 ppb MCL, and flags any system with a reported violation or exceedance.
Because cadmium sampling frequency is lower than for more heavily monitored contaminants like lead and disinfection byproducts — testing intervals vary based on system size and prior compliance history — WaterVerge’s city pages show the most recent available result and note when it was collected rather than implying real-time monitoring. Cadmium is not part of the EPA’s Unregulated Contaminant Monitoring Rule (UCMR) program, since it already carries a regulated MCL, so WaterVerge’s data comes strictly from SDWIS compliance records.
As with lead and copper, this data reflects the water system’s source and treatment performance — it does not capture what happens after water enters a home’s own galvanized plumbing. If your home was built before 1960 and has not had its supply lines replaced, WaterVerge’s city-level cadmium data should be supplemented with a tap-specific test.
If your home was built before the 1960s and still has original galvanized supply lines, cadmium impurities in the zinc coating can leach into standing water — even if your utility's source water tests clean. Flush the cold tap for 30 seconds to 2 minutes after any period of non-use, and never drink or cook with water from the hot tap.
How to Remove Cadmium
Utility-level treatment relies on corrosion control, similar to the approach used for lead and copper — adjusting pH and alkalinity, or adding a corrosion inhibitor, to reduce how much metal leaches from pipe materials system-wide. At the household level, several point-of-use treatment technologies are effective, but not all filtration is equally reliable, and certification to the correct NSF/ANSI standard is the only trustworthy way to confirm a specific product actually reduces cadmium.
| Method | Removal Rate | Certification | Best For |
|---|---|---|---|
| Reverse osmosis (under-sink) | 95–99% | NSF/ANSI 58 | Highest reduction; treats drinking and cooking water |
| Ion exchange (cation resin) | High, model-dependent | NSF/ANSI 44/53 (varies) | Whole-house or point-of-use systems |
| Activated carbon with specialized media | Up to 85–90%, model-dependent | NSF/ANSI 53 (must specify cadmium/metals reduction) | Pitcher and faucet-mount filters — check the label |
| Standard activated carbon (taste/odor only) | Not effective | NSF/ANSI 42 only | Not recommended for cadmium |
Reverse osmosis delivers the most consistent, highest-magnitude cadmium reduction of any point-of-use technology, and is the option most water treatment professionals recommend for households with a confirmed cadmium problem, whether from source water or galvanized plumbing. Under-sink RO systems certified to NSF/ANSI Standard 58 treat water at a dedicated tap, which pairs naturally with drinking, cooking, and infant formula preparation. Our guide to the best reverse osmosis systems compares current certified models and pricing.
Ion exchange systems, including some water softeners using cation-exchange resin, can substantially reduce cadmium by swapping cadmium ions for sodium or potassium ions as water passes through the resin bed. Effectiveness depends heavily on resin type and system design, so verify the specific certification claim before relying on a softener alone for cadmium reduction.
Activated carbon filters vary enormously in cadmium performance. A pitcher or faucet-mount filter certified only under NSF/ANSI Standard 42 — the standard covering taste, odor, and chlorine reduction — provides no reliable protection against cadmium. You need a filter specifically certified to NSF/ANSI Standard 53, with cadmium or general “metals reduction” listed among its verified contaminant claims. Always check the specific model’s certification sheet rather than assuming any carbon filter covers heavy metals.
Because galvanized plumbing is such a common cadmium source, two no-cost behavioral steps matter regardless of which filter you choose:
- Flush the tap: Run the cold water for 30 seconds to 2 minutes before drinking or cooking, especially first thing in the morning or after any extended period the water sat unused. This clears out the standing water that had the most contact time with galvanized pipe surfaces.
- Use cold water only: Never use hot tap water for drinking, cooking, or mixing infant formula — heat accelerates metal leaching from galvanized and other plumbing materials, the same guidance that applies to lead and copper.
What does not work: boiling water does not remove cadmium — it concentrates dissolved metals as water evaporates. Standard pitcher filters marketed only for chlorine taste improvement should not be relied on for cadmium reduction. For a full walkthrough of testing and remediation options for older plumbing, see our lead in water homeowner’s guide, much of which applies equally to galvanized-pipe cadmium and lead risk since the two often occur together in the same aging infrastructure.
Check Your City
Cadmium risk depends heavily on both your water utility’s source and treatment practices and the age and material of your home’s own plumbing. Search your city on WaterVerge to review the most recent SDWIS cadmium compliance results for your public water system, including whether any MCL exceedances have been reported.
If your home was built before the 1960s and you’re unsure whether your supply lines are galvanized, copper, or plastic, or if you rely on a private well in an area with a history of mining, smelting, or heavy fertilizer use, consider a laboratory test of a first-draw tap sample — utility-level data cannot capture what’s happening inside your own plumbing, and private wells fall outside EPA’s public water system monitoring entirely.
Frequently Asked Questions
Is cadmium in my tap water dangerous?
At the levels typically found in US public water systems — well under the 5 ppb MCL — cadmium in drinking water poses low risk to most people. The greater concern is sustained exposure over years to decades, particularly for households with older galvanized plumbing where cadmium can leach at the tap independent of what the utility delivers. Kidney damage is the primary chronic health concern.
How is cadmium different from lead in terms of risk?
Both leach from aging plumbing materials and both cause chronic organ damage with long-term exposure, but their regulatory approach differs: lead has an MCLG of zero because no safe threshold has been identified, while cadmium’s MCLG equals its MCL (5 ppb) because its primary health effect, kidney damage, is threshold-based. IARC classifies both as carcinogens, though cadmium’s cancer classification rests mainly on inhalation, not ingestion, evidence.
Does boiling water remove cadmium?
No. Boiling does not remove cadmium or other dissolved metals — it actually concentrates them as water evaporates, since cadmium has a far higher boiling point than water and stays behind in whatever remains in the pot.
How do I know if my pipes are galvanized?
A magnet will stick to galvanized steel pipe but not to copper or plastic (PEX/PVC). Galvanized pipe often shows a dull gray color and, at older joints, visible rust staining. If your home was built before 1960 and you haven’t had plumbing replaced, galvanized supply lines are a reasonable starting assumption worth confirming with a plumber or a water test.
What’s the difference between cadmium in my city’s water and cadmium from my own plumbing?
Your city’s SDWIS compliance data reflects cadmium levels in the treated water leaving the plant or entering the distribution system — it does not account for what happens as that water travels through your home’s own pipes. A utility can report cadmium well under 5 ppb while a specific home with old galvanized plumbing still sees elevated levels at the tap. Only a tap-specific test captures your actual exposure.