retaining water after exercies

today i walked for over five hours (not really for exercise, it's a long story, but it happened!).  i haven't been hungry today and have only eaten about 1600 cals while i've burned about 800 from all that walking.  but i've gained 1.3 kilo since this morning.  i know body weight fluctuates, but mine usually is the same at night as it was in the morning. 

any explanations for why i "gained" 1.3 kilo in 12 hours?  it's not TOTM for me.  i am at a loss.  maybe retaining water from exercise? 

Yes, that is quite likely the reason. It will flush out over the next day or two if you drink sufficiently.

This happens to me every week.

 I have 3 hours of dancing every Thursday night and even when I barely eat anything I weigh at least a pound more the next day... Grrrrr!

Don't worry, it's not real weight

Your best defense is to actually eat and drink enough water.