Microplastics — plastic particles smaller than 5 mm — have been detected in over 90% of bottled water samples and the majority of tap water systems tested worldwide. The average person may ingest approximately 5 grams of microplastic per week (equivalent to the weight of a credit card), though estimates vary widely by study methodology. Research into the health effects of microplastic ingestion is still in early stages, with current evidence pointing toward potential inflammatory, endocrine-disrupting, and gastrointestinal effects. This guide covers what microplastics are, how they enter drinking water, what health risks are currently understood, and how water source type affects exposure.
What Microplastics Are and How They Enter Water
Microplastics are classified into two categories. Primary microplastics are manufactured at small sizes — microbeads in cosmetics, synthetic textile fibres released during washing, and plastic pellets used in manufacturing. Secondary microplastics result from the breakdown of larger plastic items (bottles, bags, packaging) through UV degradation, mechanical abrasion, and weathering.
Microplastics enter drinking water through surface water contamination (rivers and lakes receiving plastic waste and wastewater), atmospheric deposition (plastic particles carried by wind and deposited into water catchments), and leaching from plastic water pipes and containers. Wastewater treatment plants remove 90–99% of microplastics from sewage, but the remaining 1–10% enters waterways in discharge, and the captured particles often end up in agricultural sludge that re-enters the water cycle through soil runoff.
Bottled water contains higher microplastic concentrations than tap water in most studies, likely due to leaching from the plastic bottle during storage, transport, and exposure to heat or sunlight.
What Health Risks Microplastics May Pose
Current research identifies 3 potential pathways through which microplastics may affect human health: physical particle effects, chemical leaching, and microbial transport.
Physical particle effects: Microplastic particles in the gastrointestinal tract may cause localised inflammation, particularly at sites where particles accumulate or become embedded in the intestinal lining. Studies in animal models show inflammatory responses at high exposure levels, though equivalent human data is limited.
Chemical leaching: Plastics contain additives including bisphenol A (BPA), phthalates, and flame retardants. When microplastics are ingested, these chemicals may leach into body tissues. BPA and phthalates are established endocrine disruptors — they interfere with hormone signalling, potentially affecting reproductive health, thyroid function, and developmental processes in children.
Microbial transport: Microplastic particles provide surfaces for bacteria and viruses to colonise, potentially carrying pathogens into the digestive tract that would otherwise be filtered out or destroyed by stomach acid.
The constraint is that current evidence is primarily from laboratory and animal studies. Long-term human epidemiological data on microplastic ingestion is not yet available. The WHO's current position is that microplastics in drinking water do not appear to pose a health risk at current measured levels, but acknowledges significant data gaps that require further research.
How Water Source Type Affects Microplastic Exposure
Microplastic concentrations vary significantly by water source:
Groundwater consistently shows the lowest microplastic concentrations of any source. Water drawn from deep aquifers through boreholes passes through multiple layers of soil and rock that act as natural filters, trapping particles far larger than the pore spaces in the geological substrate. Protected borehole water accessed through hand water pumps contains negligible microplastic contamination.
Tap water from municipal treatment plants contains variable levels depending on the source water and treatment technology. Advanced filtration (reverse osmosis, nanofiltration) removes most microplastics, but older treatment systems with conventional sand filtration allow smaller particles through.
Bottled water shows the highest average concentrations in most comparative studies. A major study found an average of 325 microplastic particles per litre of bottled water, compared to 5.5 per litre of tap water. The plastic bottle itself is a significant source of contamination.
Surface water (rivers, lakes, open wells) contains the highest environmental microplastic loads because it receives direct input from plastic waste, atmospheric deposition, and wastewater discharge. Communities dependent on untreated surface water face the highest microplastic exposure alongside the more immediate risks of microbial and chemical contamination.
How to Reduce Microplastic Exposure
Reducing microplastic intake from drinking water involves source selection and filtration:
Use groundwater where available — deep borehole water is the lowest-microplastic drinking water source. In developed nations, this means well water; in developing regions, this means borehole-fed pump water.
Filter tap water — reverse osmosis and activated carbon filters remove most microplastics. Standard jug filters (e.g., Brita) reduce but do not eliminate microplastic particles.
Avoid heating water in plastic containers — microwaving water in plastic or storing bottled water in direct sunlight increases leaching of both microplastics and chemical additives.
Reduce bottled water reliance — tap water filtered through a quality home system consistently contains fewer microplastics than bottled water.
The constraint is that complete elimination of microplastic exposure is currently impossible. Microplastics are present in food, air, and water throughout the global environment. The goal is exposure reduction, not elimination.
Microplastics and the Global Water Quality Divide
Microplastic contamination is a concern at every economic level, but it adds a compounding risk for communities already drinking contaminated water. In regions where families drink untreated surface water, microplastics are one contamination layer on top of bacteria, parasites, and chemical pollutants that pose far more immediate health threats.
The priority for these communities is not microplastic filtration — it is access to any clean water source at all. A hand water pump drawing from a protected borehole provides groundwater with naturally minimal microplastic content alongside the absence of microbial and chemical contamination. Addressing the most urgent contamination risks simultaneously reduces microplastic exposure as a secondary benefit.
For communities in Pakistan and Africa dependent on surface water, the health benefits of switching to clean groundwater extend across every contamination category — from the bacteria that kill today to the microplastics whose long-term effects are still being quantified.