Does reusing single-use plastic water bottles put microplastics in your water?

What's actually in it

Single-use plastic water bottles are made of PET (polyethylene terephthalate). Milk cartons use HDPE or a plastic-lined paperboard. Both shed microplastics over time. Fresh bottles shed less. Bottles that have been squeezed, warmed in a car, or reused drop thousands more particles per liter. The cap and neck are the worst spots because opening and closing grinds plastic against plastic.

Microplastics carry a payload of plasticizers, colorants, and antimony, a metal used to make PET. Once those particles are in you, they end up in blood, lungs, and placenta. The stuff doesn't stay in the gut.

What the research says

A 2025 study in Environ Monit Assess counted microplastics in popular drinking water bottles and milk cartons. Nearly every sample had detectable microplastics, with PET and polyethylene fragments making up the bulk. People who drink only bottled water take in tens of thousands more microplastic particles per year than people who drink filtered tap water.

Heat makes it worse. A bottle left in a hot car, washed in a dishwasher, or refilled with hot water gives off far more plastic than a cold bottle in the fridge. Squeezing a soft bottle also flakes the inside.

Glass and stainless steel bottles don't do this. Filtered tap water has far fewer microplastics than bottled water, not more.