I do this a lot. I do have one bottled water horror story, however. I had a 1L convenience store water bottle in my trunk bag on a day trip out to Sunset Crater then on to Grand Falls the hard way - miles of washboard road. The flimsy 1L bottle had split from all the jostling so I was out of water once I'd drained my 3 bike-mounted bottles. I was so thankful to make it back to civilization and a Navajo preacher topped off my bike bottles with "city water".

Moral of the story: If you're in the rough stuff or want to reuse the bottle a lot, pick the sturdier 2L bottle if there's an option.

I still use 1L for smooth road trips all the time, though.