Most people who switch to bottled water to avoid tap water contaminants aren’t thinking about what’s in the bottle itself. For microplastics specifically, the bottle is the problem.
The 2018 Study That Changed the Conversation
Researchers at the State University of New York at Fredonia, commissioned by Orb Media, tested 259 bottles of water from 11 brands purchased in nine countries. The brands included Aquafina, Dasani, Evian, Nestle Pure Life, San Pellegrino, and others sold internationally.
Average microplastic content: 325 particles per liter. Tap water studies from the same period found averages around 5 to 10 particles per liter in developed countries. Highest single-bottle finding in the study: 10,000+ particles per liter.
That’s a 65-fold difference between bottled and tap water on average.
Where the Plastics Come From
Bottled water microplastics don’t come from the water source. They come from the packaging.
PET plastic (polyethylene terephthalate, used in most water bottles) sheds microparticles. Opening the cap generates plastic fragments from friction between the cap threads and bottle neck. Light exposure and heat degrade PET over time, accelerating the process. A bottle that sat in a hot car for an afternoon releases more microplastics than one kept at room temperature.
The bottling process itself introduces contamination. Equipment, conveyor systems, and filling lines all shed particles. Orb Media researchers photographed fibers and fragments under microscopy that were consistent with industrial plastic rather than PET bottle material, suggesting cross-contamination during production.
Reusable hard plastic containers (Nalgene, various BPA-free options) also shed microplastics over time, especially with age, scratches, and repeated washing. They’re better than single-use PET but not equivalent to glass or stainless steel.
Nanoplastics: Smaller and More Abundant
Microplastics get the attention. Nanoplastics are smaller and more concerning.
A 2024 study published in PNAS found that a liter of bottled water contains approximately 240,000 nanoplastic particles. Nanoplastics are smaller than 1 micron (microplastics are 1 micron to 5 millimeters). At that size, they can potentially penetrate cell membranes. Research on nanoplastic health effects is still at early stages. No regulatory body has set limits for nanoplastics in drinking water.
The bottled water nanoplastic concentration from the 2024 PNAS study is orders of magnitude higher than in tap water. The same structural explanation applies: the bottle, cap, and filling process are the sources.
The Health Question
Microplastics have been found in human blood, lungs, liver, kidney, testicles, and placenta. Their presence in human tissue is now well documented. What’s not established is what harm, if any, they cause at typical exposure levels.
A 2024 study published in the New England Journal of Medicine found an association between microplastic presence in arterial plaque (carotid artery) and higher rates of cardiovascular events. Patients whose plaque contained microplastics had higher rates of heart attack, stroke, and death over a three-year follow-up period than patients whose plaque didn’t contain microplastics.
That’s an association study. It doesn’t establish that microplastics caused the cardiovascular events. It could reflect shared risk factors (people exposed to more microplastics may have other risk factors too). The research community is still working through what causation looks like here.
No government agency has set an MCL for microplastics. The EPA and WHO are monitoring research. The current regulatory position is that there’s insufficient evidence to set enforceable limits.
What Reduces Microplastics in Tap Water
Reverse osmosis removes 99.9%+ of microplastics, per a 2025 study in Nature npj Clean Water. This is because RO membranes filter at 0.0001 micron, far smaller than even the smallest microplastic particle. Any RO system physically cannot pass a microplastic particle.
Carbon block filters (the dense compressed type, not granular carbon) reduce microplastics significantly by physically trapping particles. Granular activated carbon, the loose-bed type found in most basic pitcher filters and refrigerator filters, doesn’t reliably filter microplastics.
A 2024 study from researchers in China found that boiling water reduced microplastic concentration, but through a specific mechanism: minerals in the water precipitated and physically encapsulated some microplastics, allowing them to settle. This effect is limited to hard water with high mineral content and doesn’t apply to the PFAS or chemical content of the water.
The Concrete Picture
Bottled water is not a solution to the microplastics problem. It’s a source of the problem. The packaging introduces more microplastics than you’d get from filtered tap water.
RO-filtered tap water in a glass or stainless steel container is the lowest-microplastic combination currently available to most households. The microplastics contaminant guide covers what’s known about health effects and where research currently stands.
For filter options, under-sink RO systems are the most effective point-of-use option for microplastic reduction.