Tea has long been celebrated for its health-promoting qualities—packed with antioxidants, linked to heart health, and known for its calming properties.
Now, emerging research reveals another unexpected benefit: tea leaves may play a valuable role in purifying water by naturally filtering out harmful heavy metals during the brewing process.
In a new study conducted by a team at Northwestern University in Evanston, Illinois, researchers found that the act of steeping tea could reduce levels of contaminants like lead and cadmium in drinking water. The process, known as adsorption, involves the tea leaves binding to these toxic metal ions, effectively pulling them out of the liquid.
“We found that brewing tea has the potential to remove a meaningful fraction of metal content in drinking water. The longer the tea is steeped for, the more removal you can observe,” says first author Benjamin Shindel, a PhD candidate in materials science and engineering at Northwestern.
Addressing Concerns About Tap Water Contamination
In the United States, tap water is regulated and generally considered safe. However, the issue of aging infrastructure—especially corroded lead pipes—can still pose a risk. This is particularly true in older neighborhoods, where plumbing systems may not have been updated for decades. In such cases, heavy metals can leach into the water supply, going undetected by taste, smell, or sight.
The discovery that tea leaves might help reduce exposure to these contaminants provides an encouraging new avenue for safer hydration, particularly for communities facing water quality challenges.
According to Ana Navas-Acien, MD, PhD, chair of environmental health sciences at Columbia University Mailman School of Public Health, the research opens up a new and novel way of looking at tea.
“To actually think of the tea leaves themselves as a way to adsorb the metals from the water was a very interesting finding that I don’t think is very commonly known or thought about,” says Dr. Navas-Acien, who was not involved in the research.
Putting Tea to the Test: Study Design and Methodology
To evaluate tea’s potential as a natural water filter, researchers tested a variety of teas, including black, green, oolong, white, chamomile, and rooibos. They examined both loose-leaf and commercially bagged teas to determine if packaging affected the results. The experiment involved creating controlled water samples containing known concentrations of heavy metals—namely lead, chromium, copper, zinc, and cadmium.
The team then steeped the tea in the contaminated water for varying lengths of time, from a few seconds up to 24 hours, and analyzed how much metal remained in the water afterward. This allowed them to calculate the percentage of metal ions removed by the tea during brewing.
How Tea Brewing Methods Influence Adsorption
The findings revealed several key insights about how different aspects of the tea-making process impact its ability to filter out metals:
- Type of Tea Bag Matters: The material of the tea bag played a more significant role than the type of tea itself. “The key to a successful sorbent (or molecule-collecting) material is high surface area,” the researchers noted. Cellulose tea bags—made from plant fiber—performed best in adsorbing heavy metals. Bags made of cotton or nylon adsorbed negligible amounts by comparison.
- Tea Type and Grind Have Minimal Impact: While all types of tea showed some degree of adsorption, the grind of the leaves made a slight difference. Finely ground black tea leaves were more effective than whole leaves, likely due to increased surface area available for the metal ions to bind.
- Longer Steeping Equals More Filtration: The single most important factor for adsorption was time. “Some people brew their tea for a matter of seconds, and they are not going to get a lot of remediation. But brewing tea for longer periods or even overnight — like iced tea — will recover most of the metal or maybe even close to all of the metal in the water,” says Shindel.
Why Tea Leaves Are Effective Filters
Tea leaves possess a large active surface area, making them ideal for the process of adsorption. This same quality that allows them to release flavor compounds into water so efficiently also makes them capable of binding with and trapping metal contaminants.
“Tea happens to be the most consumed beverage in the world. People don’t need to do anything extra. Just put the leaves in your water and steep them, and they naturally remove metals,” says Shindel.
The natural convenience and wide availability of tea make it a practical option for people looking to reduce their exposure to waterborne toxins without any specialized equipment.
A Closer Look at the Health Risks of Heavy Metals
Both lead and cadmium pose serious health risks, even at low exposure levels. Lead is especially dangerous during stages of brain development, such as in utero and early childhood, and is linked to cognitive impairments, kidney dysfunction, and high blood pressure in adults.
Cadmium exposure can lead to nausea, vomiting, and long-term kidney damage, and has been associated with bone fragility and cancer when inhaled over long periods.
Because these metals are undetectable by taste or smell, they can easily go unnoticed in drinking water unless tested. The Centers for Disease Control and Prevention (CDC) recommends regular water testing, especially in homes built before 1986, when the use of lead pipes was more common.
Practical Implications for Everyday Tea Drinkers
The study found that a standard cup of tea—brewed with one bag for three to five minutes—can remove about 15% of lead from the water. For people who consume tea regularly, this might translate into a small but meaningful reduction in overall exposure to heavy metals.
“If tea accounts for about one-fifth of a person’s beverage consumption, that might reduce a person’s lead intake by about 3 percent,” the authors noted. While this isn’t a silver bullet for removing all contaminants, it adds another layer of potential health benefit to an already popular beverage.
“We’re not recommending that tea drinkers change their habits or try to brew bitter tea to remove more metals. But we think it’s an interesting finding that on the margins, tea consumption might be lowering metal intake to a small degree for people who frequently drink tea,” says Shindel.
A Cup of Prevention
This groundbreaking study not only underscores the health benefits of tea consumption but introduces a compelling new way of thinking about how everyday habits can contribute to well-being. As concerns about water quality continue in various parts of the world, the notion that something as simple as steeping tea could help remove harmful metals from drinking water is both encouraging and practical.
It’s a reminder that nature often holds hidden solutions—sometimes in the very cup we’re already holding.