2 liters is a good goal to aim for. It’s more than enough for your average healthy person. It is possible to drink too much water, but unless you’re downing 2 liters in the course of an hour or something, there’s no way 2 liters of water is going to hurt you. It’s better to drink on the high side of average than the low side. 1 glass is not enough!
I’m not sure exactly how much I drink. I bring a water bottle with me wherever I go and I’m constantly taking sips from it. I probably refill it at least four or five times a day, and it’s a pretty large bottle. I personally should probably be drinking at least 4 liters a day, because of my lack of colon and because I get kidney stones. I’m probably not quite reaching that goal right now, but I think I’m close.