Techland is doing its damnedest to take the piss out of Destiny. You know, that "wow, this is really yellow, actually it's almost orange; this cannot be good for my kidneys" piss. It's running a similar drink-based promotion, and this one's designed to help you skirt renal failure.
On the heels of the reveal of Destiny's Red Bull DLC, Techland's announced a Dying Light marketing stunt that's considerably more health-conscious. Take a picture of yourself drinking a glass of water, tweet it with the hashtag "#DrinkRightDyingLight," and get a code for a new top-tier weapon.
Assuming you're in a part of the world with readily-available water, this boils down to free content. That's sure to go over a lot better than overpriced energy drinks tacked onto overpriced DLC.