Used to drink about 3l of Coca-cola a day... then I stopped smoking, gained about 15kg (>30lbs) and switched to tap water.
Then a big scandal hit when the waterworks in Bergen was infected by
Giardia, and thousands of people got really sick and put a real dent in the image of the high quality, clean, healthy Norwegian tap water. So even if I avoided the worst of the infection
(though at the time I did mistakingly wonder if I'd gotten lactose intolerant), it still put me off tap water for a while.
Recently I've drunk quite a lot of Cola Zero, and even if it cannot measure up to real Coke, it the best attempt at a diet cola, so far, much better than "second placed" Pepsi Max.
I've also started drinking some tap water again, and for pure refreshment when you're hot or just thirsty that is excellent.
Still nothing that can beat the taste and feeling of a nicely chilled Coca-cola fresh from a glass bottle on a hot day though...