I seem to be in the same boat with this. When I first wake up I am usually rather groggy. I also have a large bladder and my first response is to empty it as I do drink a lot and it's often why I wake up (the morning wood keeps it in till I reach the toilet or bottle - I usually collect it for showering / massage). I don't always take the first one but when I do I notice it wakes me up nicely. It does however usually taste rather bitter / salty in comparison to the others. If I was to take all the first urination I think it would be at least 750 ml to a litre to drink. Easily 2-3 cups. Tomorrow I will be doing another short fast and a Liver Flush so I will keep you all posted as to how it goes. I ate a few things at Christmas that aren't really good for the UT so I have been off it a few days but I think that is good thing as I have had many detox symptoms and I needed to flush my system. My kidneys have been hurting a bit too so perhaps they were overloaded a bit.
The plan tomorrow however is to drink all urination so I will be eating a healthy Diet today in preparation.