In Thailand public water pressure are too low(to reduce wear&tear in pipelinesystem) so in the pipeline mostly always just 70% water and 30% air. so he did this to trap those air in pipeline while the output on tap will look like it has more water pressure. but the truth is mostly it just make those bottle as a capacitor who deduct Air from the pipe until the pressure in the bottle is stronger than the pressure in the pipeline it will stop working automatically. then air in the bottle will drained out through the tap until both pipeline and bottle have equal pressure. like this in circle.