Heavy metals are dense metals associated with toxicity at low levels — most are hazardous to human health in any quantity. Lead is the most common example.
Yet drinking water routinely contains at least 7 common and many more uncommon heavy metals you should know about. Join us as we discuss what they are, where they come from, and how to remove them from your water supply.
If you have kids at home — please read this.
What Are Heavy Metals?
The term “heavy metal” refers to elements that:
- Have a high density from 3.5 to 7 g/cm
- Are poisonous at low concentrations
- Share the chemical characteristics of metals
That sounds cut-and-dry, but it isn’t. There is no universal definition for heavy metals. Like tomatoes — fruits we call vegetables because of how we use them — some don’t meet these strict criteria. Yet scientists consider them heavy metals because of their industrial applications and health effects.
It’s not meant to be confusing, but rather to identify potentially toxic metals in an easy-to-understand way.
How Do Heavy Metals Get into Drinking Water?
Heavy metals are natural. Present in the Earth’s crust, they’re used in a broad range of human activities from mining to electronics manufacturing.
They get into drinking water through:
1. Fossil Fuels
Burning fossil fuels spews toxic substances into the air. A common cause of metal pollution, the rain cycle returns airborne contaminants to the Earth where it falls into surface water supplies.
2. Plumbing Materials
Heavy metals have extraordinary properties that once made them ideal for plumbing materials. Strong and flexible, they were widely used in homes and underground service lines before researchers discovered some were toxic. Today, aging pipes are a primary source of metal pollutants in tap water.
3. Industrial Pollution
Industrial wastewater is a primary source of heavy metal contamination. Discharge seeps into surface runoff where it migrates into surface and groundwater supplies.
Heavy metal contamination is unfortunately ubiquitous in aquatic ecosystems and also affects human health through the aquatic life we eat. Fish from tuna to rainbow trout have high metal concentrations in their tissue.
Who Regulates Heavy Metals in Tap Water?
The Environmental Protection Agency (EPA), a department of the United States government, sets enforceable maximum contaminant levels (MCL) for health hazards in the water supply, including heavy metals. They also set non-enforceable goals (MCLG) to guide states and water treatment officials as they hammer out their own rules.
All-encompassing regulations at the federal level make little sense because not all contaminants are present in all areas — it depends on your geography and geology. Arsenic, for example, is prevalent in the northeast while mercury is more common in the mid-Atlantic states.
Common Heavy Metals in Drinking Water
These heavy metals are most water in low concentrations. But some are quick to cause metal toxicity.
#1 Mercury
Mercury occurs naturally in rock. It’s present in the environment in three forms:
Elemental Mercury
Elemental mercury is the shiny silver metal called quicksilver. Liquid at room temperature, it’s found in old thermometers, thermostats, fluorescent lightbulbs and electrical switches. In solid form, it’s stable and still used in dental fillings.
Exposure occurs when things with liquid mercury break.
Inorganic Mercury
Inorganic mercury is abundant in the environment. It combines readily with sulfur, chlorine and other elements to form inorganic salts that enter into the air and water.
Top sources include manufacturing facilities and coal-fired power plants. Airborne, occupational exposure is common.
Methyl-mercury
Methyl-mercury is the most common form of organic mercury. Air and waterborne, it’s highly toxic. Most people are exposed through drinking water or by eating fish.
The neurological effects of mercury can be devastating to the human body. Though rare, a single exposure at high concentrations can cause death. Chronic exposure at work, through tap water and contaminated food, however, is regrettably common.
Symptoms of chronic toxicity include:
- Nausea
- Vomiting
- Muscle weakness
- Impaired coordination
- Changes in vision, hearing or speech
Mercury is particularly hazardous for developing fetuses. There’s a significant positive correlation between drinking water with elevated levels of mercury and developmental disabilities in children.
The EPA and local authorities have issued advisories related to the consumption of certain types of fish. The MCL for tap water is 2 parts per billion (ppb).
#2 Cadmium
Cadmium is a lesser-known heavy metal used in the production of batteries, metallic coatings, paint pigments, plastic stabilizers, solar cells, electronics and more. Critical for the manufacture of quantum dot nanoparticles, it’s both a present and merging risk.
Few human studies have been conducted, but chronic exposure is linked to reproductive and kidney disorders. We do know, however, that cadmium affects aquatic life nationwide, and therefore, anyone higher up on the food chain.
The MCL is 0.005 mg/L or 5000 ppb.
#3 Arsenic
Arsenic is a gray metal found in the bedrock where there was a history of volcanic activity. A known carcinogen, it’s also used in rat poisons and manufacturing.
Arsenic is so common and so deadly that it’s heavily regulated in public drinking water. Wells remain vulnerable. One in ten Maine households, for example, drinks arsenic-contaminated water.
Acute toxicity is very rare. Arsenic poisoning is insidious, creeping up over time. Symptoms include:
- Garlicky breath
- A metallic taste in the mouth
- Generalized weakness
- Nervous system disorders
- Seizures
Continuous long-term exposure is fatal. The MCL is 0.1 mg/L or 10 ppb.
#4 Chromium
Chromium is a tasteless, odorless metallic element found in two forms. Trivalent chromium or chromium-3 is found naturally in the environment. An essential nutrient, we consume it in fruits, vegetables, grains and meats.
Hexavalent chromium, or chromium-6, doesn’t have a stellar reputation. It, too, occurs naturally as rainwater erodes chromium deposits, but it’s also used in factories. Poor industrial wastewater management practices pose a significant threat of chromium contamination.
Is chromium dangerous? Yes and no. Research suggests it destabilizes aquatic systems, but the jury is out on whether it causes harm to humans. The MCL is 0.1 mg/L or 100 ppb based on limited studies. Associated with high blood pressure and atopic dermatitis in humans, chromium is less toxic than most heavy metals— but more studies are needed.
#5 Copper
Copper has been on the EPA’s radar since the 1980s. Though present in the soil but uncommon in the water supply, your greatest risk of exposure comes from the copper pipes and plumbing fixtures within your home.
Regulated by the EPA’s Lead and Copper Rule, part of the Safe Drinking Water Act, copper is an essential nutrient, but high levels can cause nausea, vomiting and diarrhea. The incidence of toxicity is low below the MCL threshold of 1.3 mg/L.
#6 Iron
Chemically, iron is a heavy metal, but it’s rarely toxic. The EPA hasn’t set recommended limits for iron, but it’s grouped with more hazardous metals because of the conditions it creates in your plumbing system.
An essential nutrient, the human body uses iron to transport oxygen. But microorganisms, called iron bacteria also use iron for food, colonizing your well and pipes in the presence of an ample supply. Manganese, another heavy metal common in well water with high concentrations of iron, causes a similar problem.
Alone, iron bacteria can cause stomach aches but not diseases. It does, however, help create conditions under which pathogenic bacteria can thrive.
#7 Lead
Lead is perhaps the most dangerous heavy metal in drinking water because it’s common. Lead is used in manufacturing, but most contamination comes from pipes.
If you live in an older community, chances are your water travels through a lead service line. And pre-1980s homes may have lead pipes or lead in their plumbing fixtures.
Further reading: What does lead look like in water
High lead levels in adults causes:
- Fatigue
- Muscle weakness
- Hypertension
- Cardiovascular disorders
- Headaches
- Memory loss
- Infertility
- Miscarriage
- Seizure, coma and death
Lead poisoning in children causes:
- Irritability
- Abdominal pain
- Weight loss
- Kidney disease
- Neurological disorders
- Hearing loss
- Learning disabilities and severe developmental delays
Symptoms start late and exposure is cumulative. More common in developing countries, the toxic effects in children may be irreversible even with treatment.
Lead regulations are tricky. No level in drinking water is safe, but it will take decades and billions to remove lead from the public water supply. In the meantime, the action level is set at 0.015 mg/L. It’s less than children’s advocates wanted but realistic in the face of funding challenges.
See the: best water filters for lead removal in 2022
Should I Have My Water Tested for Heavy Metal Contamination?
Heavy metal contamination is so serious that regulatory authorities from the EPA to the CDC and the USGS are all actively involved in tracking environmental pollution. They don’t have all the answers, but they take soil samples nationwide to map the geological and geographical risks.
If you drink well water, you can log on to these sites to see maps of your area that show heavy metal concentrations. If you drink from a public water supply, your greatest risk of metal poisoning comes from your home. But your local water company is required to share the results of water testing. You’re never in the dark.
Still, the safest approach to water quality is to have your water tested. Some metal contaminants, however, are difficult or cost-prohibitive to detect with home testing. We recommend using only certified drinking water laboratories because heavy metal contamination is a serious health risk.
We recommend SimpleLab’s Tap Score test kits because they use the latest in concentrated nitric acid and hydrogen peroxide testing to ensure your heavy metal analysis is laser-accurate. Send them water samples, and you’ll get a comprehensive report including guidance on water filters. When it comes to contaminants you can’t see, smell or taste, like lead, you can’t be too careful.
How Can I Reduce My Exposure to Toxic Metals in Tap Water?
The best way to limit exposure to heavy metals is to avoid contaminated drinking water and the foods made with it. But bottled water is costly, so we recommend a drinking water filter as a more convenient, cost-effective and ecologically friendly alternative.
Filters that remove toxic metals include:
Activated Carbon Filters
Activated carbon filters target heavy metals through adsorption — a chemical process by which contaminants cling to substances with expansive surface area. Activated carbon filtration removes some but not all heavy metals depending on the type and quality of the filter used.
Whole-house carbon filters range in price from hundreds to thousands. But you can get a quality faucet filter or water filtration pitcher for less than $40.
Reverse Osmosis Systems
Reverse osmosis filters force water through a semi-permeable membrane that excludes most molecules larger than water. When combined with carbon and sediment prefilters that remove substances that can damage the membrane, RO filters fit under your kitchen sink and remove up to 99.9% of heavy metals from drinking water.
Ion Exchange Filters
Ion exchange filters use electrically charged resin to trap contaminants of the opposite electrical charge to binding sites. The best example is a water softener, but iron and manganese filters also rely on this technology.
Whole-house filters, ion exchangers purify the water throughout your home starting at around $700.
Distillation
Boiling water concentrates contaminants, but distillation removes them by capturing clean steam and condensing it back into liquid form.
Unlike other filters, however, distillers have a small capacity and can only filter a few gallons per day. Still, it’s a highly-effective, budget-friendly option with countertop units starting below $80. Performance rivals reverse osmosis filters.
The Bottom Line
We don’t want you to lose sleep over your water quality, but heavy metal contamination is an ever-present threat. Until our infrastructure is upgraded, and the many sources of contamination identified, you and especially your children are at risk. So, filter your water today and rest easier tonight.