The water from your tap may look sparkling clean, but it could contain like lead, arsenic, cadmium and chromium.

Heavy metals are everywhere. They're even in baby food. There's a way to reduce your exposure, a Northwestern University study found — brew a cup of tea using tea leaves. This simple process can effectivelyfilter out these dangerous contaminants.

Is there anything “magical” about tea leaves that gives them this super filtering ability? “I'm not sure that there's anything uniquely remarkable about tea leaves as a material,” Benjamin Shindel, PhD graduate, alumni of Northwestern and the study's first author, said in a press release. “They have a high active surface area, which is a useful property for an absorbent material and what makes tea leaves good at releasing flavor chemicals rapidly into water."

The type of tea didn't matter that much. But finely ground tea leaves, particularly black tea leaves, absorbed slightly more metal ions than whole leaves.

“But what is special is that tea happens to be the most consumed beverage in the world,” Shindel added. “You could crush up all kinds of materials to get a similar metal-remediating effect, but that wouldn't necessarily be practical. With tea, people don't need to do anything extra. Just put the leaves in your water and steep them, and they naturally remove metals.”

Shindel and his Northwestern team explored how different types of tea, tea bags and brewing methods affected adsorption of heavy metals. They tested their theory using so-called “true” teas which included black, green, oolong and white, plus chamomile and rooibos teas. In case you're not familiar with rooibos teas, they are a caffeine-free herbal tea made from the leaves of the Aspalathus linearis plant. It's also known as red bush tea or African red tea.

The researchers also created different water solutions that contained varying amounts of lead and other metals and then heated the mixture to just below a boiling temperature. Then they added the tea leaves, which had been steeping for various time intervals from seconds to 24 hours. They also used different kinds of tea bags.

After steeping, the team measured how much of the metals remained in the water. By comparing metal levels before and after adding the tea leaves, they were able to calculate how much of the metals were removed.

Here's what they found:

  • Cellulose bags did the best job of absorbing lead. Cotton and nylon bags only absorbed trivial amounts of the contaminants.
  • The longer the steep, the more metal was absorbed.
  • Tea type didn't matter that much. But finely ground tea leaves, particularly black tea leaves, absorbed slightly more metal ions than whole leaves. That's because when tea leaves are processed into black tea, they wrinkle and their pores open, creating more surface area for binding the metals.
  • Most importantly, when you're making tea, don't rush it. Steeping time turned out to be the most important element.

“You could crush up all kinds of materials to get a similar metal-remediating effect, but… tea happens to be the most consumed beverage in the world.”

“Any tea that steeps for longer or has higher surface area will effectively remediate more heavy metals,” Shindel said. “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.”

No one will deny the British are tea-loving experts. The UK Tea and Infusions Association offers the following tips for brewing the best tea:

  • Use a good quality teabag or loose-leaf tea.
  • Store tea in a cool, dry place and avoid placing it next to strongly flavored or scented foods.
  • Always use freshly drawn water when preparing tea or an herbal infusion; the hot water “energizes” the leaf and extracts all the character of the tea.
  • The water temperature for black tea should be 90º to 98ºC and around 80ºC for green tea. Check the instructions on pack.
  • To draw the best flavor out of the tea the water must contain oxygen; this is reduced if the water is boiled more than once. Only boil the amount you need — it saves energy, too!
  • Measure the tea carefully. Use 1 tea bag or 1 rounded teaspoon of loose tea for each cup to be served.

The study is published in the journal, ACS Food Science & Technology.