Most of juice is water. Water is a heavy, bulky substance that is expensive to ship. So most juices are concentrated by evaporating most of the water and leaving behind a thick liquid. Then the concentrate is shipped to wherever it needs to go, and a local bottling plant adds the right amount of water to the concentrate to produce juice again. Juices not from concentrate are more expensive (all that water was shipped the entire distance), but they’re usually said to taste a little better and the concentrating process risks losing very fragile components.