There is a lot of controversy over whether you should refill plastic bottles or not. I have known many singers (and other musicians) who claim it gives them a sore throat and general lousy health. Some sources claim it puts toxins in your body, while others claim it cultivates bacteria which can make your throat phlegmy. Many others claim this is a whole load of crap. While there has been no definitive consensus on whether this is indeed true or not I can offer some simple advice that I have been following myself. If you feel like you may be extra phlegmy or reacting poorly to filling up plastic bottles, stop doing it immediately. Some people even find Brita Water makes their throat feel a little odd. A simple solution is to buy Sigg Bottles which you can recap and reuse. Around the house, I refill empty wine bottles throughout the day which I find to be a more pleasant flavor than the metal Sigg Bottles.