greenbean replied: "If some of what you drank was Diet Coke it wouldn't be too bad, because there's not an enormous amount of caffeine in it but if you drink it all the time then that's not as good. Diet Coke itself is nothing like water- it's not just the sugar and caffeine that's bad for you in excess, the phosphoric acid that's in coke will erode the enamel in your teeth, and the general content of it which is chemicals (artifical flavouring/artificial sweeteners/preservatives etc) I'm sure you don't need me to tell you isn't in water at all. The problem with diuretics is that they make you wee more than you need to (regardless of the actual volume involved) and this will make your body retain water in an effort to balance your electrolytes, and if it can't do that then your electrolytes will get out of balance which can make you really ill. Also, water is free and Diet Coke is not, so there's another reason not to drink it so much. And, you're not having any environmental impact if you take water in a reusable bottle from home and drink that all day, rather than cluttering up the planet with all those cans and bottles. And, you're not contributing to the massive swollen coffers of in international company. And, there's no caffeine in water so you won't the caffeine buzz/caffeine crash thing, which just makes you feel like you need something with caffeine in it to perk you back up again. If basically what you're asking is "can Diet Coke be substituted with water" then the answer is no. You're missing the point if you're thinking Diet Coke must be like water because it has virtually no calories in it, like water, because that's only because it's got no sugar in it unlike water which never had any sugar in it in the first place, but Diet Coke still has all the additives, which water never had in the first place either. You need to cut down your Coke consumption, but do it gradually because you'll get caffeine withdrawal headaches if you stop it all suddenly."