Can a PET water bottle be refilled and reused?

Yes.  Single-use PET bottles can be refilled at home so long as they are washed thoroughly between uses.  It's a common misconception that refilling and reusing a PET bottle will somehow cause the bottle to degrade, release harmful substances or cultivate bacteria. P ET is a stable, inert material that doesn't biologically or chemically degrade with use, and is resistant to attack by micro-organisms.