The World Health Organisation (WHO) is to launch a review into the potential risks of plastic in drinking water.
It will assess the latest research into the spread and impact of so-called microplastics particles that are small enough to be ingested.
It comes after journalism organisation Orb Media found plastic particles in many major brands of bottled water.
There is no evidence that microplastics can undermine human health but the WHO wants to assess the state of knowledge.
Bruce Gordon, coordinator of the WHO’s global work on water and sanitation, told BBC News that the key question was whether a lifetime of eating or drinking particles of plastic could have an effect.
“When we think about the composition of the plastic, whether there might be toxins in it, to what extent they might carry harmful constituents, what actually the particles might do in the body – there’s just not the research there to tell us.
“We normally have a ‘safe’ limit but to have a safe limit, to define that, we need to understand if these things are dangerous, and if they occur in water at concentrations that are dangerous.”
Mr Gordon said that he did not want to alarm anyone, and also emphasised that a far greater waterborne threat comes in countries where supplies can be contaminated with sewage.
But he said he recognised that people hearing about the presence of microplastics in their drinking water would turn to the WHO for advice.
“The public are obviously going to be concerned about whether this is going to make them sick in the short term and the long term.”
The WHO initiative is partly in response to a study that screened more than 250 bottles of water from 11 different brands bought in nine countries – the largest investigation of its kind.
The tests were carried out at the State University of New York in Fredonia as part of a project involving original research and reporting by the US-based journalism organisation Orb Media.
Using a dye called Nile Red, which binds to free floating pieces of plastic, the university’s Prof Sherri Mason found an average of 10 plastic particles per litre of water, each larger than the size of a human hair.
Smaller particles assumed to be plastic but not positively identified were found as well – an average of 314 per litre.