Some of you may be in the habit of using and re-using your disposable water bottles, keeping them in your car or at work. Not a good idea. In a nutshell, the plastic (called polyethylene terephthalate or PET) used in these bottles contains a potentially carcinogenic element (something called diethylhydroxylamine or DEHA). The bottles are safe for one-time use only; if you must keep them longer, and keep them away from heat as well.
Repeated washing and rinsing can cause the plastic to break down and the carcinogens (cancer-causing chemical agents) can leach into the water that YOU are drinking. Better to invest in water bottles that are really meant for multiple uses. This is not something we should be scrimping on.