Canadian researchers found that some plastic tea bags threw high levels of plastic into the water.
According to a report published by the BBC, plastic materials were found widely in tap water, bottled water, and in certain foods.
WHO says these molecules in drinking water are not dangerous.
But the organization also said the findings were based on "limited information" and called for more research on the subject.
The researchers, from McGill University in Montreal, Canada, called for further investigation into the health effects of fine plastics, known as small pieces "less than 5 mm" of any type of plastic debris. What about the study?
In the study, researchers purchased four different types of commercial tea, packaged in plastic bags.
Most tea bags are made of paper, but some premium brands have switched to using some kind of plastic mesh for their products.
The researchers removed the tea, and put the empty bags in hot water up to 95 degrees Celsius. They found that one plastic tea bag left about 11.6 billion small particles and 3.1 billion smaller nanoparticles in hot water. The molecules are completely invisible to the naked eye.
"The level of particles emitted from one tea bag is several times higher than the plastic particles previously found in other foods," the study concluded.