I now filter my water & pour it into an empty plastic bottle. For recent heat, I've left space at the top & put them in the freezer for ice water.

Plastic is not as impermeable as glass. Don't plastics outgas in the sun as well? I don't drink a lot of soda & can't stand colas. When I could still get colas in glass 6 packs for company, that soda would still be fine over a year later. Now with only plastic or cans, I find one gets consumed & some time later when I open an old one, it's flat & tastes like the container. I think this is what makes an expration date on water make some sense. Someone else has mentioned that the soda bottles also seem to absorb the taste of the soda.

I don't see a problem with refilling & reusing, but long term use for storage, especially if exposed to the sun, may not be a good idea.