A steaming cup of tea has long been associated with numerous health benefits, from reducing the risk of heart disease to lowering inflammation. Now, a new study from Northwestern University suggests another unexpected perk: brewing tea may help purify water by naturally adsorbing heavy metals such as lead and cadmium.
Tea’s Natural Purification Properties
The study, published in ACS Food Science & Technology, found that tea leaves—particularly when steeped for longer periods—can trap certain harmful metals in water, preventing them from being consumed. The process, known as adsorption, occurs when a solid material captures molecules from a liquid, gas, or dissolved substance, allowing them to adhere to its surface.
“This is one of very few systematic studies that provide rational control, meaningful statistics, and nanotechnology-level sophistication brought to a seemingly mundane topic of tea brewing,” said Dr. Vinayak Dravid, the study’s senior author and a professor of materials science and engineering at Northwestern University.
How the Study Was Conducted
To test tea’s metal-absorbing properties, researchers created water solutions with high concentrations of metals, including lead, cadmium, chromium, copper, and zinc. They then brewed different types of tea—black, green, oolong, white, chamomile, and rooibos—using both loose leaves and tea bags made of various materials, including cotton, nylon, and cellulose (a biodegradable material derived from wood pulp).
Their results showed that cellulose tea bags were the most effective at removing heavy metals, while cotton and nylon bags showed minimal adsorption. The type of tea also played a role, with finely ground black tea leaves proving more effective at absorbing contaminants than whole leaves.
“When tea leaves are processed into black tea, they wrinkle and their pores open,” said Dr. Benjamin Shindel, the study’s first author. “Those wrinkles and pores, as well as a finer grind, increase surface area, enhancing the capacity for contaminant binding.”
On average, brewing a cup of tea removed around 15% of lead from drinking water when steeped for three to five minutes. The longer the tea steeped, the greater the reduction in heavy metal content.
Real-World Implications
Although the study suggests that tea could help remove some contaminants from water, experts caution that it is not a replacement for proper water filtration. Dr. Tasha Stoiber, a senior scientist at the Environmental Working Group who was not involved in the study, noted that while tea may help remove some lead, it does not eliminate other dangerous substances such as nitrates, arsenic, or PFAS (per- and polyfluorinated alkyl substances).
“I’m not sure that there’s anything uniquely remarkable about tea leaves as a material,” Shindel said. “They have a high active surface area, which makes them good at releasing flavor chemicals rapidly into water, but similar metal-remediating effects could be achieved with other materials.”
However, the study highlights how a simple, everyday habit—brewing tea—could provide small-scale water purification benefits, particularly in situations where access to clean water is limited.
“Tea happens to be the most consumed beverage in the world,” Shindel added. “People don’t need to do anything extra—they’re already drinking it.”
While tea won’t replace traditional water filtration systems, its natural ability to reduce heavy metals in water offers yet another reason to enjoy a daily cup.