[madelyn]

Doesn't the underside of bottlecaps have a plastic liner?

Plus, microplastics are a global phenomenon. Like, they're found on the bottom of the ocean.

[nikolay]

Yes, there's and most caps even have some lining - resin or pastic, I'm not sure, but there's a really small surface and most cases during transporation water won't touch it. Well, I'm idealizing things as the water from the spring most probably goes thru PVC pipes into the bottles anyway...

[trident5000]

Most likely realistic outcome is biology will be forced to adapt to plastic and its side effects rather than the genie goes back in the bottle.