Keep a close eye on the coolant header tank level. Always check it under the same conditions, preferably before you start it from cold because that's when it will be at its lowest level. When hot it will be higher.
If it doesn't go down at all over a few days use then you're fine.
From what you say I suspect it's normal, it's always surprising how much water can live in the radiator fins.
You can also try using a piece of white paper to soak some of this liquid up; if it's coolant it will be coloured (blue or red usually).