Lunk,
The big difference between plastic water bottles and plastic water pipes is that after the initial flush, a plastic pipe would be expected to not continue to generate micro/nano plastic particles in the water. The water bottles though are a one-time use and they aren't rinsed before being filled for sale, so the plastic is residue/dust created by the manufacturing process of the bottle.
That being said, I don't tend to keep bottled water very long. I can increasingly taste the plastic in older bottles of water. Maybe it's in my head though.