I'm going to a fast-food restaurant just to fill up my water bottles
Is there something wrong with your own water? I'm trying to understand why you're doing this.
I'm very strict about my water quality
Are you going to buy something while you are there. They will typically only let paying customers use their drink dispenser, even if it is just for water.
No, I just want to use the drink dispenser.
I understand it's free water, but they usually only serve paying customers so you're wasting gas money on top of that. Plus, fast food drinks are usually teeming with lots of bacteria since they're not cleaned well.