People like "new." As Don Draper once said, "it creates an itch." But what do you do to create that itch if the product never really changes? Such would be the challenge for a brand like Evian. It's water... how much does the product really change? Sure, serving sizes and distribution avenues could be altered and flavorings and extra stuff could be added, but these things, while indeed new, aren't very interesting for consumers to talk about.
But what is interesting: enlist famous designers to create Pret-a-Porter packaging.
By allowing designers to customize packaging Evian creates something new, something interesting, is able to charge a premium (around $13 each!) and enhance their brand among different audiences and distributors (such as the likes of Dean & Deluca).