I find having it measured out at the beginning of the day helps. I keep empty 750ml mineral water bottles and fill 5 of those (am on 3.5l a day!) which I then make my way through... and take one out and about with me.
Sorry but drinking 8 glasses a day is a complete myth and there is ZERO scientific evidence for it. Google it. Lots of reputable websites confirm it. When your body needs water, you feel thirsty. Don't ignore that and you are optimally hydrated.