UPDATED concentrated juice
Juice concentrate in water soluble film. Just add water.

Solution

Juice concentrate would be contained in water soluble cubes or orbs. Consumer puts one of these in a glass and simply adds normal or carbonated water to make aprox 300ml of juice. (SQUARE shape is more efficient and sustainable)

The soluble film could be like the washing pods. Here is a company that produces already one film suitable for food and liquids: "these are a transparent, odorless, tasteless films composed of a proprietary blend of food grade ingredients, offering robust mechanical properties that enables real-world usage for various food delivery applications. " http://www.monosol.com/brands.php?p=117