'Your body will hold on to water in your system if it thinks it is not getting enough.'
I think this is true. I'm not a medical worker but I'd venture to say that the body, when it gets enough, or more than enough water, starts to dump that water, too. Which is great.
I read something somewhere (wish I knew where) that explained this. It had something to do with sodium levels getting diluted or something and then the body senses the level changed and re-adjusts. Yeah, I have no idea where I got that. But it makes some sense to me that getting rid of water in your system would be a result of some adjustment process. Which works both ways - for too much or too little.