Bottled water vs filtered tap water
Is bottled water worse than filtering my own?
The verdict
Filtered tap, by a wide margin and on measured evidence. Bottled water is the single most-measured microplastic exposure there is — around 240,000 particles per litre in the 2024 PNAS work. A reverse-osmosis membrane is the only home mechanism that acts below a micron.
Polyamide membrane in a plastic housing, usually with a bladder storage tank
62% confidence
These carry different evidence grades. Aquafina is grade A and Under-sink reverse osmosis system is grade C. One component of our score is measured release, which only earns points where a laboratory has actually counted particles — so a product nobody has tested scores lower than an identical one that has been. Part of the gap you are looking at is a difference in how much anyone has looked. Why we do it this way →
Where they actually differ
| Aquafina | Under-sink reverse osmosis system | |
|---|---|---|
| Measured particle load | ~240,000/L (PNAS 2024); 93% of bottles contaminated (Mason 2018) | Unmeasured, but the membrane pore size is below the particle size |
| Where the plastic comes from | The bottle wall and cap, over months | Housings and tank bladder, over seconds of flow |
| Evidence grade | A — brand was in a tested cohort | C — membrane physics, no particle study |
| Cost per litre | Roughly a thousand times tap | Filter changes only |
Where this comparison stops being reliable
This is a comparison across evidence grades, which needs care: bottled water scores high partly because it has been measured, and RO scores low partly because nobody has counted particles in its output. The direction is not in doubt — the mechanism is a bottle versus no bottle — but the size of the gap is less certain than the numbers imply.
The full picture on each
Does Aquafina have microplastics?
Yes, and this one has actually been measured. Aquafina was one of the eleven brands in the 2018 Mason study, which found microplastic in 93% of the 259 bottles it tested across those brands, averaging 325 particles per litre.
Full score breakdown and sources →
Does Under-sink reverse osmosis system have microplastics?
The most effective home option by a wide margin. An RO membrane rejects particles far below a micron, which is the only mechanism in a domestic kitchen that acts on the nanoplastic fraction at all. The housings and tank bladder are plastic, which is the trade.
Full score breakdown and sources →
Neither of these is what you own
A comparison is between two product types. The item in your cupboard has its own packaging, its own age and its own condition. Scan it and get the same five-component score for the actual object.
Scan what I actually have