Most of us probably reuse water bottles—mainly to help the environment. Plus, it’s the easiest option when we’re heading out for a walk or doing any kind of physical activity.

We often do the same with leftover flavored water after a meal. But the truth is, this habit could actually put our health at risk.

Why are we saying this? What’s the danger?

This realization has raised some serious concerns. Recent research has found that certain plastic bottles contain chemicals—like bisphenol A (BPA)—that may be harmful to our health.

Scientists from the University of Exeter and Cambridge have discovered that BPA can lead to narrowing of the arteries, which increases the risk of heart attacks and angina.

What’s more, researchers from the National Institute of Environmental Health Sciences found that BPA has estrogen-like effects, which can negatively impact the pancreas and even cause insulin resistance.

Clearly, it’s important to pay closer attention to what we use to drink from. Let’s break it down: