Bottled water is no bargain, and plastic bottles are bad for the environment if not properly recycled.
I do agree that having some bottles on hand to re-wash and re-use is a good idea. My DD got a 12-bottle case of half-pints on sale, and has been reusing the bottles indefinitely for her 3 1/2 y.o. She keeps some filled with water in the fridge so he can help himself to a cold drink without making a mess.
She also fills some 1/3 to 1/2 full and freezes them, and tops them off with water to take with them when they go out. She and I do the same with larger bottles. We drink almost no soda and we do drink water when we go out for a meal.
If I bought bottled water on a regular basis I would be in the “poor house” in a hurry!