Bottled water – unusual complaint

[JamesE]

7 hours ago, Bluesofa said:

What happens with other products, where you can see there is a very small 'air' gap at the top of the bottle?

The real why: The plastic they use is thin. If there were air in the top it would compress as the bottles were jostled during shipment due to the thin plastic flexing. The continued flexing would cause the plastic to fail resulting in a failure and the loss of the 1000% profit. By filling it to the brim, the water, being uncompressible, becomes a structural element of the bottle. The proof is left up to the reader.

[Bluesofa]

7 hours ago, JamesE said:

The real why: The plastic they use is thin. If there were air in the top it would compress as the bottles were jostled during shipment due to the thin plastic flexing. The continued flexing would cause the plastic to fail resulting in a failure and the loss of the 1000% profit. By filling it to the brim, the water, being uncompressible, becomes a structural element of the bottle. The proof is left up to the reader.

That sounds like a reasonable answer, especially as there are six bottles packed in a plastic carrier bag. The 'bags of water' are thrown around quite a lot.
Six packs (bags) for 100 Baht delivered - 2.7 Baht a bottle.