DIY idea for used mineral water bottles

Most people nowadays prefer drinking bottled mineral water when not at home to using other sources of drinking water and I am no exception. But what do we do when the bottles get empty? I end up crushing it to ensure its not resold by spurious entrepreneurs but that surely is not a very elegant way to dispose it.

I am looking for suggestions or DIY ideas on what use can we put to these used empty mineral water bottles? Anything that can help us make good use of these rather than adding to plastic woes of our world.