Are microplastics in my tap water harmful?

The honest answer is: we don't fully know yet. Microplastics (particles under 5mm) and nanoplastics (under 1μm) have been detected in human blood, lung tissue, placentas, and breast milk. Lab studies show that plastic particles can carry endocrine-disrupting chemicals, act as vectors for other contaminants, and cause cellular inflammation at high concentrations. Human epidemiological data at the exposure levels found in tap water is still emerging. The precautionary principle suggests reducing exposure where feasible — which is what good filtration accomplishes.

How do microplastics get into tap water?

Multiple pathways: Atmospheric deposition (microplastics in air settling into source water reservoirs), degradation of plastic water infrastructure (aging plastic pipes can shed particles), plastic packaging in contact with water, and inadequate removal at water treatment plants. Conventional treatment removes a majority of larger microplastics but nanoplastics can pass through. A 2021 study found microplastics in 93% of global bottled water brands tested — sometimes at higher concentrations than tap water, due to plastic bottle degradation.

Does boiling water remove microplastics?

Partially, for hard water. A 2024 study published in Environmental Science & Technology Letters found that boiling hard water (with high calcium/magnesium) caused calcium carbonate to precipitate, trapping and removing up to 90% of microplastics in the calcite crust. Soft water showed lower microplastic removal from boiling. However, boiling also concentrates other contaminants — and the calcite crust would need to be managed. Physical filtration is a more reliable approach.

What size microplastics does an RO system remove?

RO membranes have a pore size of approximately 0.0001 microns (0.1 nanometers). Microplastics range from 1 micron to 5mm — all larger than RO pore size. A properly functioning RO membrane physically blocks all microplastic particles. Even larger particles (5–100 microns) are removed by the sediment pre-filter that comes standard with most under-sink RO systems. RO is the most complete microplastic removal method available at the consumer level.

How to Remove Microplastics from Drinking Water

Microplastics in Drinking Water: What We Know and What We Don't

Microplastics are in everything. They've been found in Antarctic sea ice, in clouds above the Pyrenees Mountains, in the deepest ocean trenches, and — as research from the past five years has made undeniable — in human bodies. A 2022 study in Environment International found microplastics in human blood for the first time. A 2023 study in Nature Medicine found them in human arterial plaque in patients who later suffered strokes and heart attacks at 4.5× the rate of those without microplastics in their arteries.

Whether microplastics at the concentrations found in drinking water directly cause these health outcomes — or are simply ubiquitous markers of plastic exposure — is an active area of research. See our guide on how reverse osmosis membranes physically block plastic particles. The science isn't settled. But the precautionary logic is clear: microplastics carry persistent organic pollutants and endocrine-disrupting chemicals as surface contamination, and effective filtration is available.

The WHO (2019) and EPA are both monitoring the science. Neither has set an MCL for microplastics — there's no regulatory standard. But independent testing consistently finds microplastics in both tap and bottled water.

Bottled Water Isn't Safer

A major 2018 study (Orb Media) tested 259 bottles of water from 27 brands in 11 countries and found 93% contained microplastic contamination — at higher median concentrations than most tap water samples. Plastic bottles shed particles as they age, especially when exposed to heat. If microplastic reduction is your goal, filtered tap water in a reusable glass or steel container is better than bottled water.

How to Reduce Microplastics: What Filtration Works

Microplastics are particles — physical objects in the water, not dissolved chemicals. This means they can be physically removed by appropriate filtration, unlike chemical contaminants that require specific media chemistry.

Reverse Osmosis (Best)

RO membrane pore size (0.0001 microns) is smaller than any microplastic particle (1+ microns). 99.9%+ removal. Also removes nanoplastics, dissolved plasticizers, and other chemicals. Any NSF/ANSI 58-certified RO system accomplishes this. The sediment pre-filter handles the largest particles before they reach the membrane.

Ultrafiltration (Excellent)

Hollow-fiber ultrafiltration membranes with 0.01–0.1 micron pore size remove microplastics larger than the pore size — which covers most particles in drinking water. Used in some under-sink filters and whole-house systems. Does not remove nanoplastics as effectively as RO.

Activated Carbon Block (Good for larger particles)

Compressed carbon block filters have tighter pore structures than granular activated carbon. High-quality carbon block filters (0.5–5 micron rating) remove a substantial portion of microplastics while also addressing chemical contaminants. NSF/ANSI 53-certified blocks are preferable. Not as complete as RO or UF.

Pitcher Filters (Limited)

Most pitcher filters use loose granular carbon with a relatively open structure. They reduce some larger microplastics but are not specifically certified for microplastic removal and provide incomplete protection at the nanoplastic scale.