All I know is I've lost 123lbs so far and drink lots of Coke Zero. Maybe I would have lost more if I'd stuck to water, but who wants to live like that??!
Mind you I had a much bigger factor involved so whatever influence drinking or not drinking it would have had was washed out completely by other things, so maybe not the best data point.
Also walked 15,000 steps the other day, for me that's crazy. Last year I averaged maybe 2-3000 a day.