Yeah, there's no need to worry too much, as the others have said...
Just treat it like a normal day, and have your packs and water as you normally would. The WI, although important, is just a snap shot of your weight at a particular time during the week... It may or may not be the lowest you've been that week, as it fluctuates so much, even from morning to night... (well, it does for me anyway!)...
It's worth remembering that a litre of water weighs 2lbs, so it
may make you a little higher on the scale in the evening... But it's only water, and it's all relative! So, it'll only be this once that the loss might show less... If you do the same thing every Tuesday before your WI, then the losses will be relative, and show as normal...
Some people choose to not drink so much water before hand... although not drinking enough on your WI day might make you retain water, making you show heavier, and also could inhibit your loss for that day (we all know the more you drink, the more your shrink!)...

...so to sabotage your loss for that day seems a shame, as it's the long term goal you're after... it's not all about what your weight is on a Tuesday night at your WI...
Whatever you decide, if you keep doing what you're doing, you're gonna keep losing like you have... the WI is just one random night... So don't worry hunny... it'll be fine!
xx