Some people like flavored/bubbly water over plain flat water. Some people do Perrier, some do LaCroix, some do Coke Zero. All of these are essentially nutritionally identical.
Really just a question of whether you think the artificial sweetener has an adverse effect on your health, which in these quantities it doesn't seem to. And if you want caffeine -- the caffeine in a liter of Coke Zero is the same as a single cup of coffee, so this is the same as a fairly normal 2 cups of coffee per day.
But the effect is mainly in sugary drinks, not diet. In fact, a study found that diet cola decreased kidney stones, although not meaningfully, so it's probably zero effect at all [1]:
> "There was a 23% higher risk of developing kidney stones in the highest category of consumption of sugar-sweetened cola compared with the lowest category"
> "Artificially sweetened sodas were marginally associated with kidney stones, with an inverse relation for colas and a direct relation for noncolas."
So no worries about your Coke Zero giving you kidney stones. The culprit seems to be the fructose, rather, which Coke Zero doesn't contain:
> "Higher consumption of sugar-sweetened soda was associated with a higher incidence of kidney stones, which may be because of the fructose content. Fructose has been shown to increase the urinary excretion of calcium, oxalate, and uric acid, thus increasing the risk of stones."
The large drink size at a major gas station chain around here is about 1.8 liters. It's a popular size. Some people may drink one over multiple days, but that's not the norm. And that's not the largest size any gas stations around here have.
Some "medium" sodas at fast food joints are over a liter, these days.
People who drink a lot of soda, in the US, really DRINK A LOT OF SODA.
Consider also that it's been the norm for years, in the US, to have free refills on soda at restaurants (with waiters eagerly topping them off constantly) and that many fast food places have self-serve soda that's either explicitly or de facto unlimited refill, if you go inside to eat rather than using the drive-through.
Some people like flavored/bubbly water over plain flat water. Some people do Perrier, some do LaCroix, some do Coke Zero. All of these are essentially nutritionally identical.
Really just a question of whether you think the artificial sweetener has an adverse effect on your health, which in these quantities it doesn't seem to. And if you want caffeine -- the caffeine in a liter of Coke Zero is the same as a single cup of coffee, so this is the same as a fairly normal 2 cups of coffee per day.