Bottled Water Has More Microplastics Than Tap — But How Much?

Bottled water is often sold as the clean, safe choice. A 2024 study of Spain’s five top-selling bottled water brands measured what’s actually suspended in it — and found microplastics at a mass concentration roughly two to three orders of magnitude higher than tap water analyzed in the same lab. [Scientific Reports, 2024]

That sounds alarming. But the same study estimates the daily dose you’d absorb from drinking it is measured in nanograms per kilogram of body weight — a level the authors describe as probably negligible to human health. [Scientific Reports, 2024]

Both things are true at once. This is the tension worth understanding: bottled water is meaningfully dirtier than tap, and the dose is still very small. Here’s what the researchers found and where the honest uncertainty lies.

What the study actually measured

The researchers tested still, low-mineralization water sold in 1.5 L single-use PET bottles — the most common format in Spain — from the five best-selling brands, together representing about 40% of that market segment. They sampled 45 L per brand, 225 L in total, all bottled at source at their respective springs. [Scientific Reports, 2024]

To mimic normal handling, each bottle was filtered in three 0.5 L aliquots, with the cap removed three times and recapped twice. Particles were identified by micro-Fourier Transform Infrared Spectroscopy (micro-FTIR), a method that confirms a particle’s chemistry rather than just counting stained specks. [Scientific Reports, 2024]

What sets this work apart is that it reported mass concentration, not just particle counts. As the authors note, obtaining mass concentration is not trivial and can produce severe errors if particle size and shape are ignored — but it is the number that actually matters for estimating exposure. [Scientific Reports, 2024]

1.61 µg/L

The numbers

Across the five brands, the study found average mass concentrations of 1.61 µg/L (range 1.10–2.88) for microplastics and 1.04 µg/L (range 0.43–1.82) for artificial cellulosic particles. By count, the median was 0.73 microplastics per liter and 1.70 cellulosic particles per liter. [Scientific Reports, 2024]

The particles were small. The median size was 93 µm for microplastics and about 77 µm for cellulosic particles. The smallest microplastic detected was a fiber just 12.5 µm across; the largest was a polyethylene fragment measuring 765 × 257 µm. [Scientific Reports, 2024]

Interestingly, cellulosic particles were more numerous but weighed less overall, because they skewed toward smaller sizes. That’s why microplastics dominated the mass despite being outnumbered. [Scientific Reports, 2024]

Where the plastic came from

Chemistry offers a clue to origin. Of the 81 confirmed microplastic particles, the composition was dominated by polyester (64 particles) and polyethylene (12), with small numbers of polyamide, polystyrene, polypropylene and polysiloxane. [Scientific Reports, 2024]

That pattern lines up with the packaging. PET bottles are a polyester, and all the caps were made of polyethylene. Nearly all the polyester fragments were white or transparent — consistent with the bottle itself — and 5 of the 11 PE fragments matched the colors of the caps. [Scientific Reports, 2024]

Bottled versus tap: the real headline

The most useful comparison in the paper is one many microplastic studies can’t make cleanly. In earlier work, the same team measured municipal drinking water from several Spanish cities and found average concentrations of 12.5 microplastics per cubic meter and 45.5 ng/L by mass. [Scientific Reports, 2024]

That’s two to three orders of magnitude below the bottled water figures reported here. And because both datasets came from the same laboratory, using essentially the same methodology across a similar size range, the comparison is genuinely apples-to-apples — a rare thing in this field, where different size cut-offs make most studies impossible to line up. [Scientific Reports, 2024]

The authors are direct about what this implies: tap water is not only cheaper and lower in plastic waste and carbon footprint, but also rigorously monitored by health authorities. Their findings, they write, support the argument in favor of municipal drinking water wherever it’s an option. [Scientific Reports, 2024]

The dose, and why it’s probably small

So bottled water is dirtier. Does that mean it’s harmful? The study’s exposure math says probably not.

Using Spanish per-capita bottled water consumption of about 65 L per year, the estimated daily intake works out to 4 ng/kg of body weight for adults and 18 ng/kg for children. Those figures would rise about tenfold for someone drinking 2 L of bottled water every day. [Scientific Reports, 2024]

4–18 ng/kg/day

The authors judge that it’s very unlikely this ingested plastic could harm humans, because it represents a concentration several orders of magnitude lower than levels shown to damage cells in laboratory models. [Scientific Reports, 2024]

The honest caveats

A careful study says where its own conclusions stop — and this one does.

There’s also a measurement blind spot. This method resolved particles down to about 15 µm. But the particles most likely to be absorbed through the gastrointestinal tract are in the few-micron range or below — mostly nanoplastics under 1 µm — which fall outside standard spectroscopic detection. There is general agreement these should form as larger plastics weather and fragment, but they’re very hard to monitor, so the smallest and potentially most relevant fraction isn’t captured in these counts. [Scientific Reports, 2024]

For perspective, the authors note the bottled water levels are broadly similar to what a glass of water might pick up from indoor airborne fallout over 20 minutes — a reminder that plastic exposure is diffuse and everywhere, not unique to any one container. [Scientific Reports, 2024]

What to actually do with this

The practical read is not “bottled water will hurt you.” On this study’s numbers, the dose is small. The practical read is that bottled water buys you no purity advantage over tap — it carries substantially more plastic, at meaningfully higher cost and environmental burden, while tap water in a monitored municipal system is both cleaner on this measure and continuously tested. [Scientific Reports, 2024]

If your tap water is a safe, regulated supply, the evidence here favors it. And if you want to minimize particles from packaging specifically, the two clearest contributors in this data — the PET bottle and its PE cap — are exactly what a single-use plastic bottle is made of. [Scientific Reports, 2024]