The amount of water used to produce a single-use water bottle can be up to 3 times higher thant the actual amount of water in the bottle. Considering that startling fact along with the reality that 44% of single-use bottle water is municipal tap water which has undergone further purification, there really is no logical reason to buy single-use water bottles.
The folks at Wheels For Wishes put together an infographic about the environmental impact of single-use plastic bottles, and includes tips for reducing water bottle usage as well as facts about plastic pollution in oceans and rivers to help encourage you to consider the source when hydrating.