There's no sugar in any of that. Or, trace amounts. It's all "zero" and "diet".

I buy bottled water for two reasons. The reason I started buying it was that I wanted to drink more water and less of everything else (I was using a ketogenic diet and there's some question about whether some artificial sweeteners cause an insulin response, and to what degree that would partially defeat the point of the keto diet).

Most of the time during most days I'm in front of some screen or another, with a glass of Diet Mountain Dew or Coke Zero nearby, and I only really pay attention to the drink when I have it in hand and notice that it's empty, whereupon I get up and refill it. This process keeps me drinking enough not to be dehydrated during the day (much more than enough, obviously), but if I don't do this, then I will at first be distracted by not finding my nearby drink, which pulls me out of whatever I'm working or playing on. This would be fine if it happened every thirty minutes, but it happens basically as soon as I stop thinking about it, which is difficult to work through. After I've adjusted to that, or if I'm in an environment in which I don't expect a drink to be nearby, I have the opposite problem, where I can sit in the same position typing and mousing for far too long. So, having a drink nearby prevents dehydration and soreness, by keeping me drinking unconsciously and prompting me to get up and walk around every thirty minutes or so.

Now, at this point you are probably thinking, "No problem! Just fill the glass with tap water and everything's the same!" In practice, however, that turned out not to be the case. For whatever reason, I was unsuccessful at training myself to drink water this way. Instead, I would find myself dehydrated and stiff with a full glass of water nearby.

At some point about five years ago, though, I found that if I had a small bottle of water (a half-liter, say) instead of an open-top glass of water, I drank that automatically and only noticed when it was empty. So, rather than fighting whatever part of me is uninterested in open glasses of water, I just bought a bunch of 0.5L bottles. Since I just put them next to my desk, I don't actually get up to refill anything, but drinking one every 45 minutes or so will force me to get up and walk in any case, so it's all good.

At first I spent some time refilling these bottles rather than buying new, but it was more trouble than it was worth: trying to train myself not to toss them, trying to be gentle (they're quite fragile), washing, filling, and drying them, keeping track of one or more containers (the plastic they come wrapped in is not a reusable container), and worst of all, keeping track of whether I need to do a refill or will run out during an upcoming stretch of work... I'm willing to pay a few bucks a week to just not have any of that.

So, I still do some of that, but have returned to drinking a lot of soda, as I mentioned, rather than 12-16 0.5L bottles every day. A 12-pack of them lasts me several days, now.

The other reason I still buy them is that sometime while I was drinking them almost exclusively I got in the habit of keeping one or two by my bedside, which solved the wake-up-with-dehydration-headache problem I had for the previous ~20 years, without any further conscious attention.

Probably too much detail. But that's why.