Hiya,
I'm on about 4litres a day, the litre bottle is a godsend and helps you really see how much you can get through...
One way I try and do when am boggled by the thought of how much water we have to get through a day, is try and have so much within a timed period... For instance I know I need to drink 1 x 1 litre bottle between 8am and 11am, then another between 12noon and 2pm, another between 3pm and 6pm, and a final one between 7pm and 10pm. I figure breaking it down like this, 3 hours to drink one litre of water should be more than do-able, right! Plus giving myself little 'breaks' where I don't need to think about drinking the water, even for an hour helps me 're-charge' ready for the next glugging session!
It really does help your skin tho too!!
Another way I've heard is treat it like medicine, it HAS to go down so grin and bear it and know it's making you 'better'?!