Brewing tea is a ritual as old as civilization, a moment of calm amid the storm of daily life. But scientists now say that it might be doing more than just waking us up and providing comfort — it could be purifying our water, too.

A new study from Northwestern University reveals that tea leaves naturally remove toxic heavy metals from water as they steep. The researchers found that lead and cadmium — dangerous contaminants that can pose serious health risks — cling to the surface of tea leaves, effectively reducing the levels of these metals in the final brew.

“We’re not suggesting that everyone starts using tea leaves as a water filter,” said Vinayak P. Dravid, the study’s senior author and a materials science expert at Northwestern. “But our work highlights the unrecognized potential for tea consumption to passively contribute to reduced heavy metal exposure in populations worldwide.”

A Natural Filtration System

The researchers set out to explore how different types of tea, brewing methods, and even tea bags affect the removal of heavy metals. They tested a variety of teas — black, green, oolong, white, chamomile, and rooibos — by steeping them in water spiked with known concentrations of lead, chromium, copper, zinc, and cadmium. After steeping, they measured how much of the metals remained in the water.

The results were pretty amazing. Finely ground black tea leaves performed best, adsorbing more metal ions than whole leaves.

“When tea leaves are processed into black tea, they wrinkle and their pores open,” explained Benjamin Shindel, the study’s first author. “Grinding up the leaves increases surface area even further, providing more capacity for binding.”

But the most significant factor was time. The longer the tea steeped, the more contaminants it removed. A five-minute brew reduced lead concentrations by about 15%, while steeping overnight removed even more.

“Some people brew their tea for a matter of seconds, and they are not going to get a lot of remediation,” Shindel said. “But brewing tea for longer periods — like iced tea — will recover most of the metal or maybe even close to all of it.”

Tea Bags Matter

Empty cellulose bags — made from biodegradable wood pulp — adsorbed significant amounts of heavy metals. Meanwhile cotton and nylon bags did almost nothing. “Cellulose has a higher surface area, which means more binding sites for metal ions,” Shindel said. “Nylon tea bags are already problematic because they release microplastics, but cellulose bags are a better choice — they’re natural and effective.”

This is particularly relevant as concerns grow over microplastics in tea. While cellulose bags may release tiny fibers, Shindel noted that these are harmless. “That’s just fiber, which our body can handle,” he said.

The researchers estimate that a typical serving of tea can remove about 15% of lead from drinking water. Over time, the cumulative effect across populations could be notable. Heavy metals like lead and cadmium are toxic even at low levels. These metals are linked to a range of health problems, including heart disease, stroke, and cognitive decline. 

“Across a population, if people drink an extra cup of tea per day, maybe over time we’d see declines in illnesses correlated with heavy metal exposure,” Shindel said. “Or it could help explain why populations that drink more tea may have lower incidence rates of certain diseases.”

Not Miraculous but Very Helpful

Let’s get something straight. This doesn’t mean that you can use tea as a reliable solution to serious contamination. If you’re concerned about heavy metals in your water, you need some advanced filtration tech.

However, the researchers acknowledged that the study points to promising avenues for developing sustainable water filtration methods, particularly in regions where access to clean water is poor. Tea is the most consumed beverage in the world after water, enjoyed in countless varieties and traditions. 

For now, tea drinkers can sip with a little extra peace of mind — knowing that their daily brew may be doing more than just warming their hands. It could be helping to clean their water, one steep at a time.

The findings appeared in the journal ACS Food Science & Technology.