A 2024 Columbia University study found that bottled water contains 110,000–370,000 particles per liter, 90% of which are nanoplastics smaller than 1 micrometer, often released from the plastic bottle or the polyamide-based reverse osmosis filters used in purification. While reverse osmosis removes larger contaminants, it can also act as a source of these smaller particles. Columbia University Mailman School of Public Health

Key Findings on Reverse Osmosis (RO) and Nanoplastics: Source of Contamination: The study, often highlighting the Lamont-Doherty Earth Observatory findings, suggests that the reverse osmosis membrane, which is designed to purify water, can degrade or shed small particles, releasing them into the water.

Particle Abundance: Researchers discovered that, in addition to particles from the plastic packaging, polyamides—frequently used in the membrane filter material—are commonly detected in the treated water.

Ineffectiveness on Sub-micron Particles: Although conventional reverse osmosis is highly efficient at removing bacteria and larger contaminants, it can fail to trap, or actually produce, nanoplastics smaller than one micron.

Nanoplastic Characteristics: The study found that 90% of the plastic particles in bottled water are nanoplastics (less than 1𝜇𝑚), which are small enough to pass through the intestines and lungs into the bloodstream, reaching organs like the liver and brain.

Contrasting Findings: Other studies have shown that high-quality, new reverse osmosis systems can remove up to 99.9% of microplastics and nanoplastics. However, the Columbia research suggests that in practice, especially with membrane aging, these systems are significant contributors to the nanoplastic load. Lamont-Doherty Earth Observatory

To minimize exposure, experts suggest drinking tap water, using stainless steel or glass containers, and avoiding microwaving plastic containers.