If I understand, you're asking how long it takes for the water weight to go away?
Some of us do, for some mysterious reason, bloat up when we first start exercising seriously. The amount of time it takes to lose that water weight varies from person to person. My advice is watch your sodium intake and drink plenty of water. Avoid diet soda too. Sometimes it causes water to stick around as well.
So, be sure to get your 8 glasses of water a day (maybe even a bit more).