The World Health Organization (WHO) in Geneva said that plastic particles in drinking water are not a major health threat.
Most micro-plastics that are swallowed with drinking water leave the body again after they pass through the digestive system, the WHO said in a report summarizing the results of several scientific studies.
"We are not worried in any way," Bruce Gordon, a water expert at the organization, told a news conference before the report was published.
"We found that there was a significant safety margin between the expected absorption of chemicals and levels that could be considered harmful."
The organization called on countries to do more to invest in water treatment systems in general to remove harmful microbes that cause nearly half a million deaths each year from diarrhea.
There are an estimated 2 billion people around the world who drink contaminated water, she said. However, the WHO stressed that consumers and governments should reduce the overall use of plastics to protect the environment.