Why would anyone buy bottled water? My god, water here in Western NY from the Erie County Water Authority costs $2.81 per THOUSAND gallons. 1 thousand gallons!! Two dollars and eighty one cents. Think about it. Good grief.
It's not a mystery. It's not the water you are paying for. It's the packaging and the convenience. Seems simple enough. Having your thirst quenched on the go is worth $1.25, regardless of how many gallons of tap water you can buy with that.