The less water you drink, the more it holds on to, because the body definitely NEEDS that water, and will do what it can to hold on to what it's got (including making you dehydrated, in the name of saving water for your body to use. Ironic, huh ?). It works similiarly with food. Don't eat enough and the body thinks you're starving, slows down your metabolism and voila, no weight loss even though you're constantly hungry.

Since starting this WOE I always thought I was drinking enough water, more or less, then one day I drank at least a gallon of it. I was running to the bathroom all the time, and when I wasn't there I'd be drinking because I was thirsty (dry mouth etc) or running to fill my water bottle. Almost craving it, the way eating one potato chip will lead you to eat the whole bag, or 3 cookies makes you want the whole row of oreos (or more).

That's when I realized "This is how much water I should be drinking every day".

As for measuring, I use a regular metal stanley retractable tape measure (tho I've only measured my stomach), and it seems to do fine. I don't think it would matter much if you held your breath, or expelled it all first, so long as you're doing it the same way every time. Consistancy rules in things like this.

Hope this helps,
Jeff