I wouldn't cut down the day before if I were you ... you'll get rid of any excess overnight and in the morning. You could actually inhibit your loss slightly doing that IMO.
I don't have my usual half litre when I wake up on weigh-day, just a few sips. Then I only have 1 hot drink whereas I'd normally have about 3 while I'm 'coming to' and I have a mousse instead of a shake. When I've been weighed I make up for what I haven't had as soon as I can.
Whatever you do don't go less that about 2.5lts - that would almost definitely have the opposite affect to what you want! x