Weight / Fat loss

I don't pretend to understand this- I imagine that the majority of the short term fluctuations are purely to do with hydration?

78kg yesterday morning, 77.5kg this morning.

Seems like a lot- although I suppose half a litre against the volume of the whole body is fairly trivial

My boss (very big danish guy) had a bet on with some friends. Who could loss the most (as a % of original weight). He basically did a bit of running and cut out snacks. But the easy win was not taking on fluids for the whole day of the weigh-in. Reckons it earnt him 1.5 - 2kg.