It depends on where you go.
Onsite, water tastes just fine (usually), but if you wander offsite you might realise that your drink tastes funny.
For example, some restaurants near crossroads (Cici's pizza is the one that pops up instantly) use tap water for their soda fountain, and even their iced tea. Even coke smells like ... I don't know what it smells and tastes like, the closest I can come up with is : sewers
Dasani also has a taste that needs some getting used to. I personnally don't like it at all.
Good point on MIO. I use the "market pantry" brand from Super Target. It's the same as MIO, only cheaper. It comes in small squishable bottles or powder. It's calory free, but needs to be added to ice cold water for the best taste.