I keep a 1.5 litre bottle of water on my desk - between 8:30 and 11:00 it's gone, then refill, takes me until an hour before I go home (don't want any accidents on the bus) then another 1.5 litres before 8:00 p.m. - after that a diet/caffine free coke for a treat (2 x weekly only). It seems like a lot but if you have the bottle always in front of you, it becomes second nature just to drink it.