Water retention when starting new workout regimen

Hey y'all!
So, for several weeks now I've gone to the gym and mostly done basic cardio (stationary bike and elliptical), but recently I've had a friend helping me to do weights, circuit training, and pretty much just an all around better workout. I've read that it is fairly common to have water retention and sore muscles when starting up a routine like this when your body has never really done something like it before.

I guess my main question is, how long can I expect this water retention to last, if that's what it really is? We only started doing the more rigorous and wider range of stuff last week so I'm not expecting some overnight (or even over-week) miracle by any means. I also know the number on the scale isn't the be all and end all, but it can really become discouraging to put so much effort into the workouts and not see the number on the scale decrease.
Thanks for any insight!