Unless you're stranded on a desert island, you should not throw empty glass bottles in the water. But you SHOULD apparently grind up those bottles, mix the ground glass with lime and caustic soda, and put that in the water to clean out toxic heavy metals.
The U.K. has backlogs of brown and green glass, because there's less recycling demand for the colored bottles than there is for clear ones. Now Dr. Nichola Coleman of the University of Greenwich has discovered that the unwanted glass can be used to filter water. The mixture of glass and caustic materials, heated at over 200 degrees, produces the mineral tobermorite, which can absorb heavy metals out of waste water and underground water reserves.
Coleman is looking into using the glass to form barriers that keep contaminated water away from the clean stuff. This is currently done with cement, but making tobermorite out of glass produces way less carbon. That would make this win-win situation — recycling orphaned glass and cleaning water supplies — into a rare win-win-win.