Yep 1 litre= 2lbs in weight.  But don't think for a second that if you drink less you will weigh less.  If your body is starved of water (either pure water or what is in food) it will retain everything it gets (leading to weight gain), whereas the more you drink the more you will flush through your system.  Many people on the forum have said that the more you drink the more you lose overall.
 
If you are worried about weigh-in, try to get your 4 litres in with a good hour to spare before WI- most of it will have disappeared down the porcelain bowl before you get weighed!
 
My experience is the same now as it was on Atkins- when in ketosis and providing you drink enough you will pee mightily- I get up and go twice in the night and am continuing to lose weight.  When I am not losing weight or gaining weight, I only pee once in the night and not so much, so I guess that proves something!
 
Keep drinking! (wish they had a drowning/glugging smiley to add here LOL)
Kx