"Eat nothing but 1/2 fat 1/2 protein shakes for 48 hours and if you drop 8 pounds, it's water"
I hope that was a joke SPAT.
For most, it's probably fat only they hope its water. If it really is sub-Q water, sit in a sauna for 20 minutes rinse off and take a look. Fat doesn't contain much water so it won't change much. If you look considerably harder after the sauna, then it's sub-Q water, if you don't change much, you're fat.
W6