Boiling hard tap water trapped up to 90% of added plastic particles in Chinese tests
Researchers in China removed up to 90% of added nano- and microplastics from tap water by boiling it and filtering the residue. Removal climbed with water hardness, and the plastic was spiked into the samples, so a kitchen result will depend on the local supply.
The Scientist · Science desk
Bar chart of nanoplastic precipitation efficiency on boiling: 34 percent at 80 mg/L of calcium carbonate, 84 percent at 180 mg/L and 90 percent at 300 mg/L.
Nanoplastic precipitation efficiency on boiling, by calcium carbonate level
| Item | Value | Claim |
|---|---|---|
| Calcium carbonate, 80 mg/L | 34% | 7 |
| Calcium carbonate, 180 mg/L | 84% | 7 |
| Calcium carbonate, 300 mg/L | 90% | 7 |
What happened
- Zimin Yu of Guangzhou Medical University and colleagues tested soft and hard tap water in 2024, boiling each sample and then filtering out the precipitate.
- In hard water, heating forces calcium carbonate out of solution onto the plastic, and the limescale crust traps the fragments.
- Soft water, which holds less dissolved calcium carbonate, still lost roughly a quarter of the added plastic.
- The researchers say the crust-bound plastic can be strained out with a filter as simple as the stainless steel mesh used for tea.
Why it matters
- What it limits constraint In soft water roughly three quarters of the plastic stayed put, so the 90% figure belongs to the hardest water tested.
- What it costs cost The equipment is a kettle and a mesh. The open cost is habit, since the authors say boiled-water drinking prevails in only a few regions.
- What it limits constraint The tests count particles removed. How damaging the plastic is to the body is still uncertain, so a removal percentage is not yet a measured health benefit.
The hardness gradient is the part of this result we would trust most. For nanoplastics, precipitation efficiency was 34 percent at 80 mg/L of calcium carbonate, 84 percent at 180 and 90 percent at 300 [7]. Hardness rose 3.75-fold across that range [20], and removal rose 56 percentage points [16]. Fifty of those points were already in hand by 180 mg/L [17], so the curve flattens at the top.
"Our results showed that nanoplastic precipitation efficiency increased with increasing water hardness upon boiling," the team wrote [10]. We think a rising series fits the limescale explanation better than a single before-and-after comparison would.
A drinker cares about what is left. After boiling and filtering, about 66 percent of the nanoplastic remained at 80 mg/L and about 10 percent at 300 mg/L, a 6.6-fold difference in residue [18].
The plastic was spiked in, and the stress test only raised the dose: when the team added even more nanoplastic, the particles were still reduced effectively [11]. Past studies have measured four different polymers in potable tap water: polystyrene, polyethylene, polypropylene and polyethylene terephthalate [14]. The thing this doesn't tell you is whether a gradient measured on added particles carries over to that mix. ScienceAlert's account does not say which polymers were added, at what concentration, or whether removal was counted by particle number or by mass.
We'd commit to the chemistry and hold the household benefit open. Zimin Yu and colleagues framed the payoff as a potential. They said: "This simple boiling water strategy can 'decontaminate' NMPs from household tap water and has the potential for harmlessly alleviating human intake of NMPs through water consumption," [12].
What to watch
- A test on unspiked municipal tap water that reports polymer types and whether removal is counted by particle number or by mass.
- Results at hardness levels between 80 and 180 mg/L, where most of the gain occurred.
- Any measurement of how much crust-bound plastic returns to the water when limescale flakes off in a kettle.
Clarity's read
What the record supports and how the coverage leans. The claims behind it follow.
Reality
- Evidence50
- Adoption
- Not scored
- Hype gap+20
- Incentives
- Not scored
- Confidence45
Claim ledger
Ranked by verification strength, evidence, and original report placement.
- [1]
In 2024 a team in China ran tests on both soft water and hard tap water, which is richer in minerals.
- [2]
The team added nanoplastics and microplastics to the water, boiled it, and then filtered out the precipitates.
- [3]
In some cases up to 90 percent of the nano- and microplastics were removed by boiling and filtering, though effectiveness varied with the type of water.
- [4]
The researchers quoted are biomedical engineer Zimin Yu of Guangzhou Medical University and colleagues.
- [5]
A greater concentration of nano- and microplastics was removed from hard tap water, which forms limescale (calcium carbonate) as it is heated.
- [6]
Limescale forms on the plastic's surface as temperature changes force calcium carbonate out of solution, trapping the plastic fragments in a crust.
- [7]
Nanoplastic precipitation efficiency was 34 percent at 80 mg/L of calcium carbonate, 84 percent at 180 mg/L and 90 percent at 300 mg/L.
- [8]
Even in soft water, where less calcium carbonate is dissolved, roughly a quarter of the nano- and microplastics were removed.
- [9]
The researchers say the lime-encrusted plastic could be removed with a simple filter such as the stainless steel mesh used to strain tea.
- [10]
"Our results showed that nanoplastic precipitation efficiency increased with increasing water hardness upon boiling," the team wrote.
- [11]
To stress-test the strategy, the researchers added even more nanoplastic particles, which were effectively reduced in number.
- [12]
"This simple boiling water strategy can 'decontaminate' NMPs from household tap water and has the potential for harmlessly alleviating human intake of NMPs through water consumption," biomedical engineer Zimin Yu and colleagues said.
- [13]
The authors wrote that drinking boiled water is often regarded as a local tradition and prevails only in a few regions.
- [14]
Past studies have measured fragments of polystyrene, polyethylene, polypropylene and polyethylene terephthalate in potable tap water.
- [15]
It is still not certain exactly how damaging microplastics are to the human body.
- [16]
Nanoplastic removal rose by 56 percentage points between 80 mg/L and 300 mg/L of calcium carbonate.
- [17]
Fifty of those 56 percentage points were reached by 180 mg/L.
- [18]
After boiling and filtering, about 66 percent of nanoplastic remained at 80 mg/L and about 10 percent at 300 mg/L, a 6.6-fold difference in residue.
- [19]
In soft water roughly three quarters (about 75 percent) of the nano- and microplastics stayed in the water.
- [20]
Water hardness rose 3.75-fold from 80 mg/L to 300 mg/L.
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Sources
1 independent publisher whose own reporting we read for this story.
- sciencealert.comThere's a Surprisingly Simple Way to Remove Microplastics in Your Drinking Water
1 article · October 16, 2026
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