Because my body screams bloody murder if I don’t…? It’s not nice to suffer from a dry throat then drink 1,2, 3, 4, 5 glasses of water and it doesn’t help! I am a hedonist and simple enough. I am (really) hungry, I eat. I am thirsty, I drink.
I am surely not exactly normal regarding thirst, I reach the near unbearable phase super quickly. No idea why.
I don’t remember my childhood much but I changed anyway. I get overheated easily and I need water all the time. It makes perfect sense that a human should be without water for hours but it’s very unpleasant for me. It happens when I am busy (well, hooked on the Net) and it’s horrible… I do very much to avoid that! Drinking is nothing, I would do much, much more 
Never cared about other people’s opinion if it’s about my business 
I actually CAN survive 90 minutes without water even while walking - but any running or a hot day and it’s no good. So yep, I bring my water bottle for my 45 minute walkings (and usually not use it but I like to be safe. I can get super parched in no time). Not to my 10 minutes walking/running though…
I drink my own tap water, sometimes carbonated water, they refill the bottles.
I usually drink when I get quite thirsty (and that happens so so often). And sometimes for fun but I am nearly always thirsty so they overlap…
I can’t overhydrate, my body is just that smart, it seems.
I eat little salt as I like it that way.
So I stick to whatever I am doing now 