Complex sentence: Both the water and natural carbonic gas are captured independently and in the bottling process, the carbonic gas is added so that the level of carbonation in bottled Perrier is the same as the water of the Vergèze spring.
Split into simpler sentences: Both the water and natural carbonic gas are captured independently and in the bottling process. The carbonic gas is added so that the level of carbonation in bottled Perrier is the same as the water of the Vergèze spring.