Heavy metals
One test covers the whole group of metals, and for most municipal homes the news is good: arsenic, cadmium, mercury, and the rest usually come back at or below the level a lab can detect. The screen earns its place by confirming clean and by catching the rare real finding. Where the science is strongest, arsenic, the health-based goal sits far below the legal limit.
Science and Health line for arsenic
0.004 ppb
The federal limit for arsenic is 10 ppb. The health-based level is 2,500x lower.
Heavy metals: what is it, and where does it come from?
Heavy metals and metalloids that can reach a home tap at health-relevant levels include arsenic, cadmium, mercury, antimony, barium, beryllium, selenium, thallium, nickel, and aluminum. Lead and hexavalent chromium have their own pages. They arrive by three routes. Some dissolve out of the rock an aquifer sits in: arsenic, selenium, beryllium, barium.
Some enter a water source from industry or farming: cadmium, mercury, nickel, antimony. And some leach from older in-home pipes and fittings, such as cadmium from pre-1960 galvanized pipe and nickel from some fixtures. For most homes on treated municipal water, levels in this class run low.
The reason to test is to confirm that and to interpret the exception when one shows up.
Heavy metals: why does it matter?
Arsenic carries the clearest evidence.
At the high exposures seen in Taiwan, Bangladesh, Argentina, and Chile, inorganic arsenic causes bladder, lung, and skin cancer. It is also linked to cardiovascular disease, diabetes, and effects on child development.
The World Health Organization holds that no exposure level is entirely safe and that concentrations should be kept as low as reasonably possible. Cadmium accumulates in the kidneys over a half-life measured in decades and, at the high exposures behind Japan's Itai-itai disease, damaged bone and renal function. Ingestion is the route that matters here.
These ions are large and charged and pass poorly through intact skin, so showering is not the concern it is for the byproducts of chlorinating water.
California's health-based goal for arsenic is 0.004 ppb, set at a one-in-a-million lifetime cancer risk from bladder and lung cancer. The legal limit is 10 ppb, a 2,500x gap, and the federal health goal is zero.
CA OEHHA, Public Health Goal for Arsenic in Drinking Water (2004)
In a national survey of residential drinking water, arsenic averaged about 1.7 ppb and only 1.5% of samples exceeded the 10 ppb federal limit, with private wells running far higher than public supplies.
The World Health Organization labels its 10 ppb arsenic guideline provisional because of the practical difficulty of removing arsenic, and holds that no exposure level is entirely safe.
Arsenic, cadmium, beryllium, nickel compounds, and hexavalent chromium are all classified by IARC as Group 1, carcinogenic to humans, on strong human evidence at occupational and high environmental exposures.
Heavy metals: what do we grade it against?
Our Science and Health lines for heavy metals are 0.004 ppb for arsenic, 0.04 ppb for cadmium, 0.1 ppb for thallium, 1.2 ppb for mercury (inorganic), and 12 ppb for nickel. Each card below names where its number comes from, and the table sets every published level for heavy metals, including the legal limit, beside the source that set it.
Science and Health line, Arsenic
0.004 ppb
California's public health goal, one extra cancer per million people over a lifetime
Science and Health line, Cadmium
0.04 ppb
California's public health goal
Science and Health line, Thallium
0.1 ppb
California's public health goal
Science and Health line, Mercury (inorganic)
1.2 ppb
California's public health goal
Science and Health line, Nickel
12 ppb
California's public health goal
Arsenic
Health-based level 0.004 ppb one-in-a-million cancer riskLegal limit 10 ppb CA + federal MCL; federal MCLG is 0Legal limit 2,500x the health lineSource: CA OEHHA PHG, 2004
Cadmium
Health-based level 0.04 ppb kidney + boneLegal limit 5 ppb CA + federal MCLLegal limit 130x the health lineThallium
Health-based level 0.1 ppbLegal limit 2 ppb CA + federal MCLLegal limit 20x the health lineMercury, inorganic
Health-based level 1.2 ppbLegal limit 2 ppb CA + federal MCLLegal limit 1.7x the health lineNickel
Health-based level 12 ppbLegal limit 100 ppb CA MCL; federal limit remanded 1995, never replacedLegal limit 8.3x the health line
The levels for heavy metals, as a table
| Contaminant | Health-based level | Legal limit | Source (health-based) |
|---|---|---|---|
| Arsenic (ppb) | 0.004 one-in-a-million cancer risk | 10 CA + federal MCL; federal MCLG is 0 | CA OEHHA PHG, 2004 |
| Cadmium (ppb) | 0.04 kidney + bone | 5 CA + federal MCL | CA Water Boards MCL/PHG table, 2025 |
| Thallium (ppb) | 0.1 | 2 CA + federal MCL | CA Water Boards MCL/PHG table, 2025 |
| Mercury, inorganic (ppb) | 1.2 | 2 CA + federal MCL | CA Water Boards MCL/PHG table, 2025 |
| Nickel (ppb) | 12 | 100 CA MCL; federal limit remanded 1995, never replaced | CA Water Boards MCL/PHG table, 2025 |
The Science and Health line is where we flag. We set it from the health research, and it is never looser than any legal limit. Legal limits are enforceable compromises that also weigh what treatment costs. Your report grades to the Science and Health line.
Every metal on a home water test, one by one
Our home water test reports 26 metals, and chromium-6 takes a test of its own. Each metal below keeps its own Science and Health line, from 0.004 ppb for arsenic to 4,000 ppb for strontium. Most come from the ground your water passed through; lead, copper, cadmium, nickel and zinc usually come from your own plumbing.
The fix. Reverse osmosis at the kitchen tap is the fix for most of these metals at once. Each row says where it is, and where we have no certified household fix to name.
| Substance | Science and Health line | Why it matters | The fix |
|---|---|---|---|
| Aluminum | 600 ppb | At high intake it can build up in bone and brain in people with kidney disease. Natural in rock and soil; many treatment plants also use an aluminum-based settling agent. | Reverse osmosis. |
| Antimony | 1 ppb | Long-term exposure at high levels can raise blood cholesterol and lower blood sugar. Refineries, fire retardants, ceramics, electronics and solder. | Reverse osmosis. |
| Arsenic Full page: Arsenic | 0.004 ppb | Causes cancer, so no amount is risk-free; its Science and Health line sits below what labs can measure. Natural in rock, most often in groundwater. | Reverse osmosis. |
| Barium | 1,000 ppb | Long-term exposure at high levels can raise blood pressure. Natural deposits, drilling waste and metal refineries. | Reverse osmosis. |
| Beryllium | 1 ppb | Long-term exposure at high levels can damage the intestines. Metal refineries, coal burning and electronics; rarely found in tap water. | Reverse osmosis. |
| Boron | 1,000 ppb | At high doses it harms reproduction and development in animal studies. Natural in groundwater near oceans, volcanic rock and borax deposits. | We have no certified household fix to name for it. |
| Cadmium | 0.04 ppb | Builds up in the kidneys and damages them over years. Corroding galvanized pipe and some faucet parts, plus natural deposits. | Reverse osmosis. |
| Chromium, total Lab reports may say: Chromium (Total), Total chromiumFull page: Hexavalent chromium (chromium-6) | 50 ppb | The total does not say how much is chromium-6, the form that causes cancer. Steel and pulp mills, plating and natural deposits. | Reverse osmosis. A chromium-6 test shows how much of the total is the harmful form. |
| Chromium-6 Lab reports may say: Chromium (hexavalent), Hexavalent chromium, Cr-VIFull page: Hexavalent chromium (chromium-6) | 0.02 ppb | Causes cancer; its Science and Health line sits below what labs can report, so a confirmed detection is flagged. Industrial discharge and natural deposits. It takes its own test. | Reverse osmosis. |
| Cobalt | 70 ppb | Part of vitamin B12; high doses affect the blood and thyroid. Natural in rock and soil; also coal and oil burning. | We have no certified household fix to name for it. |
| Copper Full page: Copper | 0.3 ppm | It can cause nausea and stomach upset; California set its line to protect infants, children and pregnancy. Your home's copper pipe and brass fixtures, most in water that sat overnight. | Reverse osmosis or a carbon filter, either one certified for copper by name. Running the tap first is only a stopgap. |
| Iron | 300 ppb a comfort flag for pipes and taste, never a health flag | Not a health concern at tap levels; it stains sinks and laundry and tastes metallic. Natural in groundwater, from weathering rock and soil. | We have no certified household fix to name for it. |
| Lead Full page: Lead | No safe level | No amount is known to be safe; in children it can slow development and learning. Your home's plumbing: lead solder, older brass fixtures and lead service lines. | Reverse osmosis, or a carbon filter certified for lead under NSF/ANSI 53. |
| Lithium | 10 ppb | EPA is measuring it in water systems nationwide, but has not set a health line yet. Natural in groundwater from certain rocks and brines. | We have no certified household fix to name for it. |
| Manganese Full page: Manganese | 100 ppb | At high levels it can affect the developing brain; bottle-fed infants are the most sensitive. Natural in groundwater. | Reverse osmosis. |
| Mercury Lab reports may say: Mercury (inorganic) | 1.2 ppb | Long-term exposure at high levels damages the kidneys. Natural deposits, refineries, factories, landfills and farm runoff. | Reverse osmosis, or a carbon filter certified for mercury. |
| Molybdenum | 40 ppb | A nutrient in food; at high doses it affects the kidneys and blood in animal studies. Mostly food; water near mining can carry more. | We have no certified household fix to name for it. |
| Nickel | 12 ppb | The most common effect is a skin allergy in people already sensitive to it; high doses affect the kidneys and liver. Nickel- and chrome-plated faucets and stainless fittings, most in water that sat overnight. | Reverse osmosis. |
| Selenium | 30 ppb | Long-term exposure at high levels causes hair and nail loss, numb fingers or toes, and circulation problems. Natural deposits, refineries and mines. | Reverse osmosis. |
| Silver | 130 ppb | Mostly cosmetic: large amounts over years can turn skin blue-gray. Natural in trace amounts; plumbing is not a notable source. | We have no certified household fix to name for it. |
| Strontium Lab reports may say: Strontium (stable) | 4,000 ppb | At high levels it can impair bone growth in children. Natural in rock and soil. | Reverse osmosis. |
| Thallium | 0.1 ppb | Long-term exposure at high levels causes hair loss and harms the blood, kidneys, intestines and liver. Ore processing, and electronics, glass and drug factories. | Reverse osmosis. |
| Tin | None set | Most exposure comes from canned food, not water; no agency sets a drinking-water line. Tin-lined cans and industry; a minor source in water. | We have no certified household fix to name for it. |
| Titanium | None set | Considered low in toxicity when swallowed; no agency sets a drinking-water line. A natural mineral in rock and soil. | We have no certified household fix to name for it. |
| Uranium Lab reports may say: Uranium (by weight)Full page: Radionuclides (uranium, radium) | 20 µg/L | Long-term exposure at high levels harms the kidneys and raises cancer risk. Natural deposits, more often in groundwater. | Reverse osmosis. |
| Vanadium | 50 ppb | It affects development in animal studies; no harm is shown in people at typical levels. Natural in rock; also steel making and fossil fuels. | We have no certified household fix to name for it. |
| Zinc | 2,000 ppb | Large amounts upset the stomach; years of high intake can cause anemia and lower good cholesterol. Galvanized (zinc-coated) pipe, plus natural trace levels. | We have no certified household fix to name for it. If it comes from galvanized pipe, replacing that pipe removes the source. |
What helps against Heavy metals?
The approaches below are the ones people use for Heavy metals at home. Each entry says what it does and what it cannot do, and not every one helps.
Direct fixes
Reverse osmosis at the kitchen tap (NSF/ANSI 58)
Rejects most heavy metal ions by size and charge exclusion. Arsenic rejection is typically above 90% for both arsenite and arsenate, and the same membrane handles cadmium, mercury, nickel, antimony, beryllium, and the rest of the class.
Carbon block filter (NSF/ANSI 53)
Useful for chlorine, taste, and some organics, and some blocks carry a mercury-reduction certification.
Carbon block alone does not remove arsenic, cadmium, or the dissolved heavy metals as a class. For arsenic specifically, RO or an arsenic-rated adsorbent is the right tool, not carbon.
Bigger retrofits
Whole-house point-of-entry treatment
Treats every fixture in the home.
Not the right primary choice for heavy metals. The exposure route is the water you drink at the kitchen tap, and dermal absorption during bathing is poor, so point-of-use at the tap targets the actual exposure.
Free and behavioral
Test before you treat
A single kitchen-tap sample covers 15 to 25 metals at once and is already bundled into mid-tier residential panels, so the class is a check you already get rather than a paid add-on. Confirm what is actually present before installing anything.
Most of this class is a screen you want to come back boring.
On a typical treated municipal supply it does, and confirming that is part of the value: knowing what is clean is as useful as knowing what is not. The screen exists for the exception, an older home with galvanized pipe, a source drawing on the wrong aquifer, so that a real finding gets read precisely instead of missed. For arsenic we use the health-based goal, because the legal limit was set by what treatment can achieve rather than by what is safe.
Common questions about Heavy metals
Should I worry about heavy metals in my tap water?
For most homes on treated municipal water, no. Standard municipal treatment removes the dissolved forms reasonably well, so the class usually reads low or non-detect. Testing confirms that for your specific home and catches the rare exception, such as an older home with pre-1960 galvanized pipe.
Why is the health goal for arsenic so much lower than the legal limit?
California's health-based goal for arsenic is 0.004 ppb, set at a one-in-a-million lifetime cancer risk, while the legal limit is 10 ppb. The federal limit is also 10 ppb, a feasibility compromise, even though the federal health goal is zero. The World Health Organization calls its matching 10 ppb guideline provisional because arsenic is hard to remove at scale.
Does a carbon filter remove arsenic?
No. A standard carbon block leaves arsenic and the other dissolved metals in the water. Reverse osmosis at the kitchen tap is the effective point-of-use option, with arsenic rejection typically above 90%. Some carbon blocks add a mercury-reduction certification, but that does not extend to arsenic.
Is showering in this water a concern?
Not for heavy metals. These ions are large and charged and barely cross intact skin, so the dominant residential exposure route is drinking the water, not bathing in it. That is why point-of-use treatment belongs at the kitchen tap rather than on the whole house.
Do I need a separate paid test for heavy metals?
Usually not. Mid-tier and higher residential water panels already bundle the class: one kitchen-tap sample, run on the standard lab method (ICP-MS), covers 15 to 25 metals at once. Choose a panel that includes it and there is nothing extra to pay.
Sources cited for Heavy metals
Every number on this Heavy metals page traces to one of the 9 sources below: 1 peer-reviewed, 6 government or regulatory.
Government & regulatory
- CA OEHHA, Public Health Goal for Arsenic in Drinking Water (2004)
- California State Water Resources Control Board, MCLs/DLRs/PHGs table (updated September 2025)
- US EPA, National Primary Drinking Water Regulations (inorganic chemicals)
- ATSDR ToxFAQs (US Agency for Toxic Substances and Disease Registry): aluminum, boron, cobalt, molybdenum, nickel, silver, strontium, tin, vanadium and zinc
- US EPA, 2018 Edition of the Drinking Water Standards and Health Advisories Tables (EPA 822-F-18-001)
- California State Water Resources Control Board, Notification and Response Levels overview (June 2026)
Institutional & standards