Microplastics

Microplastics and the even smaller nanoplastics are tiny fragments of plastic now found in practically all drinking water, bottled water more than tap. They have been reported in human brain, liver, kidney and placenta, but what they do there is still unknown: the evidence for harm comes from animal and cell studies, not from people.

Don't make bottled water your daily source; fill a stainless steel or glass bottle from a filtered tap instead. Beyond that, the health case for going further rests on unknowns.

What they are

Microplastics are plastic fragments under 5 mm across; nanoplastics are under 1 µm (a thousandth of a millimetre). The common ones are polyester, polyethylene, polypropylene and polystyrene, and they turn up in both tap and bottled water.

How much is in your water

An earlier survey of 259 bottles across 11 major brands found signs of plastic particles in 93% of them, averaging about 325 particles per litre.^[1] A 2024 study, using a laser-imaging technique that can see far smaller particles, pushed the count two to three orders of magnitude higher: bottled water averaged roughly 240,000 particles per litre, about 90% of them nanoplastics — small enough that they could cross biological barriers.^[2]

Treat that headline number as directional, not exact. A published critique argues the study's procedural blanks — clean laboratory water run through every step — carried as much plastic as the bottled water, and that the plastic it found most was nylon-like polyamide rather than the bottle's polyethylene terephthalate (PET), which points to contamination. That makes the absolute count unreliable even if the broad conclusion holds; the original authors dispute the critique.^[3]

Either way, bottled water tends to carry more than tap, and part of it comes from the packaging and bottling: in the bottle survey, the most common confirmed plastic was polypropylene, the material of the cap.

Tea bags are a second source

The bag can shed plastic too. Tea bags heat-sealed with polypropylene release very large numbers of micro- and nanoplastic particles into the cup when brewed, roughly ten times more than plain cellulose bags, and human intestinal cells take those particles up in the laboratory.^[4]^[5] There is no human outcome data and no regulatory limit. Loose leaf, a metal infuser or a plain unbleached paper bag avoids the plastic for free; see Tea.

Where they end up in the body

Plastic fragments have been recovered at autopsy from human brain, liver and kidney, and the particles in the brain were largely nanoscale shards.^[6] Other groups have reported them in placenta^[7] and in lung tissue, where the authors put the route down to breathing rather than swallowing.^[8] A further group reported plastic particles in the blood of 22 donors, a result other researchers have contested.^[9]

What they do there: unknown

Finding a particle is not the same as finding harm. The evidence that particles cross the gut lining, that particles lodged in tissue drive chronic inflammation, or that they carry hormone-disrupting plastic additives such as bisphenols and phthalates into the body comes from animal and cell experiments. A systematic review of the field concludes that direct evidence of health effects in humans is still scarce.^[10]

So the evidence is strong that they are in drinking water, moderate that they reach human tissue, and weak on what any given dose does to health.

What removes them

Both reverse osmosis and ultrafiltration remove microplastics; the difference between them is in what else they remove. See Reverse osmosis, and Water for the wider picture of what is in drinking water.

What to do

Skip daily bottled water. It typically carries more particles than tap, partly from the packaging itself.
Use a reusable stainless steel or glass bottle filled from a properly filtered tap.
Brew tea loose or in plain paper bags rather than plastic-sealed ones.
Hold the alarming numbers loosely. The particle counts are uncertain, and so is what they mean for health.