If you live in Mexico City and you buy garrafones, you did a reasonable thing. The advice is everywhere: don't drink the tap water. So you switched to the 20-liter bottle, and you stopped thinking about it, along with most of your neighbors in Roma Norte, Condesa, and every other colonia in CDMX.

Bottled water carries its own problem, one researchers have only recently been able to measure properly.

What the research found

In January 2024, a team from Columbia University and Rutgers published a study in the Proceedings of the National Academy of Sciences. They used a technique called stimulated Raman scattering microscopy, which can spot plastic particles far smaller than older methods could detect.

They found an average of about 240,000 plastic particles per liter of bottled water. Roughly 90% of those were nanoplastics: particles small enough that earlier studies simply couldn't see them. The count was ten to a hundred times higher than previous estimates. Seven common plastics turned up, including PET (what most bottles are made of), polystyrene, and PVC.

Separate work published the same year found that tap water in some regions carried 200 to 300 times less plastic than bottled water from the same area. Research from Ohio State, sampling near Lake Erie treatment plants, found bottled water held about three times the nanoplastic particles of treated municipal water.

Why bottled water carries more

This surprises people, so it's worth being clear about the mechanism: the plastic mostly comes from the container itself, shed a little at a time.

Every time a bottle is squeezed, opened, refilled, warmed in a delivery truck, or left in the sun, a little more plastic sheds into the water inside it. A garrafón that's been reused many times, transported around the city, and stored who-knows-where has had a lot of opportunities to shed. The bottle is the source.

What we don't know yet

A lot of writing on this topic overstates what's known, so it's worth being careful here.

The health effects are not established. Researchers have found microplastics in human blood, lungs, placentas, and other tissue. That tells us the particles get into the body. It does not tell us what they do once they're there. The research on health outcomes is early, and anyone claiming otherwise is ahead of the evidence.

The measurement itself is debated. After the Columbia study came out, other researchers published a formal critique in the same journal, arguing the method needed better controls to rule out plastic contamination from the lab itself. The original authors published a reply defending their approach. That exchange is normal science working as intended, and it means the number 240,000 is best read as an early estimate from a new technique rather than a settled figure.

The direction is much better established: multiple independent studies, using different methods, keep finding more plastic in bottled water than in treated tap water. The precise multiple varies. The pattern doesn't.

Where a water filter fits

If the plastic is coming from the bottle, the fix is skipping the bottle entirely.

Filtration works on size. Our ultrafiltration systems use a membrane rated to 0.01 microns (10 nanometers), which is physically smaller than the vast majority of particles in that research. Reverse osmosis goes considerably further, down to about 0.0001 microns.

Nanoplastics are defined as anything under 1,000 nanometers, and that range extends below 10. An ultrafiltration membrane blocks most of what's been measured, but not every particle at the very smallest end. Reverse osmosis effectively does. That's a real difference between the two tiers, and it's the kind of thing we'd rather tell you before you buy than after.

The bottom line

Nobody should panic about this. The evidence that plastic particles harm humans is still incomplete, and we're not going to pretend it's settled.

But the reasoning that sent you to garrafones in the first place (avoid the risk you can't control) points somewhere else once you know the numbers. Tap water in Mexico City is treated at the source; the real risk is what happens in old building pipes and rooftop tinacos afterward. That's a problem you can fix at your own tap. The garrafón trades it for a different exposure, plus the cost, plus carrying the thing up your stairs.

Filtering your own tap water addresses the plumbing problem and the plastic one at the same time.

If you want to see what that costs, our Drinking Water Systems comparison lays out all four options side by side, and the water savings calculator will tell you what you're currently spending. Or send us your building and your water habits, and we'll walk you through which tier makes sense for you.

Sources

  • Qian, N., Gao, X., Lang, X., et al. “Rapid single-particle chemical imaging of nanoplastics by SRS microscopy.” PNAS, January 2024.
  • Materić, D. “Nanoplastics measurements must have appropriate blanks.” PNAS, 2024, and the authors' published reply.
  • The Ohio State University, research on nanoplastic content in bottled versus treated drinking water, 2024.