Researchers have found tiny plastic particles in tap water, bottled water and even human blood. If you want fewer of them in the water you drink, the microplastic filter you choose matters. This guide covers what microplastics are, what research has found so far, and how to choose a system that fits your home.
What are microplastics, and where do they come from?
Microplastics are usually defined as plastic pieces from about 1 micron up to 5 millimeters, or 5,000 microns. Nanoplastics are even smaller, under 1 micron. There is no single official size definition. Researchers believe nanoplastics enter the body more easily than larger particles, though the data are still limited.
Most plastics do not biodegrade. Weathering breaks them into smaller and smaller pieces, and EPA names food wrapping, tires and synthetic textiles among the sources. A 2018 study of 159 tap water samples from around the world, including US cities, found human-made particles, mostly fibers, in 81% of them. Conventional treatment plants remove most microplastics, with studies reporting 70 to over 90 percent removal, but some still reach the tap.
Bottled water is not a way around them. A 2018 study found signs of microplastics in 93% of 259 bottles from 11 brands, and a 2024 study of three brands estimated about 240,000 plastic particles per liter of bottled water, about 90% of them nanoplastics.
What research has found so far
Research on health effects is still early. The FDA says current evidence does not show a health risk at the levels found in food, and the WHO reached a similar view for drinking water in 2019. Both call for more research. Here is what studies have reported:
- Found in human tissue: small studies have detected microplastics in samples of lung, liver, kidney and placenta. What that means for health is not yet known.
- In blood: a pioneering 2022 study of 22 healthy volunteers measured plastic particles in human blood.
- In artery plaque: a 2024 study in the New England Journal of Medicine found plastic in the carotid artery plaque of 150 of 257 surgery patients. Those patients had more heart attacks, strokes and deaths over about 34 months, though the authors say this does not prove plastic was the cause.
- Plastic additives: some plastics are made with BPA or phthalates, chemicals NIEHS studies as endocrine disruptors.
- Inflammation: lab studies suggest some microplastics can promote inflammation in cells. Whether they do so in people is still being studied.
Reducing what reaches your glass at your own tap is a simple step you control.
Why reverse osmosis is our first pick
Microplastics are solid particles, so a filter's pore size matters most. Reverse osmosis has the finest pores of any common home filter type, about 0.0001 micron according to the CDC. For scale, a human hair is about 70 microns wide, roughly 700,000 times wider than a reverse osmosis pore.
Our Thunder under sink systems pair a 0.02 micron ultrafiltration membrane with a reverse osmosis membrane: two barriers, both far finer than microplastic particles, with carbon prefiltration ahead of them and a coconut carbon polish after. Reverse osmosis sends some water to drain as it works. Learn more about what reverse osmosis is and how ultrafiltration works.
Best water filters for microplastics by installation type
- Under the kitchen sink: for drinking and cooking water, an under sink reverse osmosis system filters right at the tap. Thunder systems come standard with a 100 gallons per day membrane, and pump models keep pressure steady. They need a drain connection and should be installed by a licensed plumber.
- On the counter: our countertop reverse osmosis system connects to most kitchen faucets with a diverter, with no under sink plumbing. It makes up to 50 gallons per day at about 60 psi and less at typical faucet pressure, so keep a pitcher filled.
- For the whole house: whole house reverse osmosis delivers reverse osmosis filtered water to every tap, sized to your household from 300 to 7,000 gallons per day.
- A lighter option: SMART filtration adds 5 micron stages to our SMART multimedia: a carbon block on Double configurations, and a carbon block plus a sediment cartridge on Triple configurations, SMART whole house and Eagle. Those stages trap particles larger than 5 microns. Eagle adds a final sub-micron ultrafiltration membrane. For the smallest particles, reverse osmosis is the stronger choice.
- Microplastics and PFAS together: reverse osmosis covers both. Read reverse osmosis for PFAS.
Pitchers and carbon filters
Filters that rely on carbon alone are made to improve taste and reduce some chemicals, not to stop the smallest particles. In a lab study, filters with a membrane barrier performed best. If you use a pitcher today, an under sink or countertop reverse osmosis system adds a membrane barrier.
Your next step
You cannot control the plastic in the environment, but you can choose what filters the water at your tap. Not sure where to start? Get a free recommendation from our specialists, or try our filter recommendation page.
