Ya know, I used to think that also. Now however, after contracting an urinary tract infection from re-using my old drinking water bottles, I now use my bottles at a maximum for one day before taking them home and sterilizing them (which you are NOT supposed to do using hot water). I drink a LOT of filtered water daily, without exaggerating 3-4 gallons daily (I work outside in the Az. heat) and I have a bad habit of leaving my bottles sitting on my office desk overnight. I usually make sure they are drained but human nature being what it is I sometimes forgot to empty them completely. No more! 72 hours of not being able to get 5 foot from a bathroom and still not being able to empty your bladder is a damned fine lesson!