What are microplastics, and why are they in drinking water?
Microplastics are plastic particles smaller than 5 millimetres. They come from the breakdown of larger plastic items, synthetic textiles, tyres, and industrial processes. Once released, they spread widely through air, water, and soil.
In drinking water, microplastics can originate from:
- Source water (rivers, lakes, groundwater)
- Water treatment and distribution systems
- Packaging, especially plastic bottles and caps
- Handling and storage, such as heat, friction, and repeated opening
Bottled water vs tap water: what does the research suggest?
Bottled water
Several studies have found higher numbers of microplastic particles in bottled water compared with tap water. A significant share of these particles appear to come not from the water source itself, but from the plastic bottle and cap, released through:
- Mechanical stress (transport, squeezing)
- Opening and closing the cap
- Heat exposure (sunlight, hot cars, warehouses)
More recent research also points to very small particles (micro- and nanoplastics) that were previously undetectable, which may increase estimated exposure from bottled water.
Tap water
Microplastics have also been detected in tap water, but generally at lower concentrations than in bottled water. Modern water treatment processes, such as coagulation, filtration, and sedimentation can remove a large proportion of particles, though not all.
The World Health Organization (WHO) has reviewed the available evidence and concludes that:
- Microplastics are present in both tap and bottled water
- Current drinking-water treatment substantially reduces particle levels
- There is no clear evidence of adverse health effects at typical exposure levels, although data gaps remain
Practical takeaways: how to reduce exposure via drinking water
Without waiting for perfect evidence, there are a few low-effort, reasonable steps that can reduce potential exposure, without alarmism.
1. Choose tap water when it’s safe to do so
In most high-income countries, tap water is strictly regulated and routinely monitored. Choosing tap water:
- Likely reduces microplastic intake
- Reduces plastic waste and environmental pollution
- Is cheaper and lower-impact overall
2. Avoid heat and sunlight with bottled water
If you do use bottled water:
- Don’t leave bottles in hot cars or direct sunlight
- Avoid reusing single-use plastic bottles, heat and UV exposure can increase particle release from plastic packaging.
Key sources & further reading
- World Health Organization (2019). Microplastics in drinking-water.
- WHO (2019). Microplastics in drinking water: Information sheet.
- Al-Mansoori et al. (2024). Synthetic microplastics in UK tap and bottled water. Science of the Total Environment.
- Koelmans et al. (2022). Microplastics in drinking water: Occurrence and human exposure. Environmental Pollution.
- Pivokonsky et al. (2020). Occurrence of microplastics in raw and treated drinking water. Science of the Total Environment.
- Systematic review: Microplastics in drinking water – methods, occurrence and research needs. Environmental Pollution (2024).
