On average, in 93% of bottles, they found more than 10 pieces of plastic thicker than a human hair and hundreds of smaller pieces that the researchers and outside experts believe are probably plastic as well.

The researchers tested 250 bottles of water—from nine countries and 11 brands. They dropped a red dye in each, which stuck to the plastic and glowed when passed under a certain light. Some bottles were so full of plastic that, to count the particles, the researchers called on a former astrophysicist, who shared his tactics for counting stars and galaxies in a crowded sky.

With the Flint lead crisis still fresh in our memories and contaminated tap water detected across the country , bottled water may seem like an appealing alternative. But a recent study of bottled water , conducted by the journalism organization Orb Media, found that almost every major brand of bottled water is contaminated with particles of plastic.

“It’s not about pointing fingers at particular brands; it’s really showing that this is everywhere, that plastic has become such a pervasive material in our society, and it’s pervading water—all of these products that we consume at a very basic level.”

Sherri Mason, a professor of chemistry at the [State University of New York in Fredonia], conducted the analysis and told BBC News: “We found [plastic] in bottle after bottle and brand after brand.

According to these findings, a person drinking an average amount of water from bottles could be consuming anywhere between hundreds and tens of thousands of microparticles a day.

Mason said the finding is alarming but not necessarily catastrophic. Little research exists on the topic and people don’t yet know much about how small pieces of plastic might interact with the body—either physically or chemically.

Some experts say it is at least cause for concern. Jane Muncke, chief scientist at the Food Packaging Forum, a Zurich-based research organization, told Orb Media that most of what is understood about ingesting plastics comes from models, not experiments, and that these don’t account for things like possible chemical interactions from the plastic.

“There’s so many unknowns here,” she said. “That, combined with the highly likely population-wide exposure to this stuff—that’s probably the biggest story here. I think it’s something to be concerned about.”

However, others believe that our bodies are well-adapted to passing non-digestible objects through our systems, and speculate that these small bits of plastic may have little impact.

Most bottled water companies stood by their methods for testing and filtering water, and experts still recommend bottled water where tap water is unsafe to drink.

It will take further research to know exactly what to make of the findings, but what’s clear is that despite its better reputation, bottled water is not necessarily purer than the tap.