When you’re thirsty, hopefully you reach for plain water, not a sugary, calorie-rich vitamin water, soda, or even (unless you need the calories) real juice. But should you turn on the tap or open a bottle? It's unfortunate that fear of pollutants has made us avoid drinking tap water, which on average is safer and cleaner than bottled water.
Another good reason not to drink bottled water is that plastic bottles contain chemicals called plasticizers that leach into the water given time and heat. If you want a water bottle to carry around, just use a glass one, i.e. a used tonic water bottle, or dump the plasticizer-rich water out of a plastic bottle and fill it with fresh tap water.
Of course now the water isn’t sterile, and bugs will eventually grow, so just refill your bottle with fresh water every morning. Don’t leave your water bottle in a hot car for a long time- if the bottle has been opened, the heat will encourage bugs to grow, and opened or not, heat will help leach plasticizers into the water.