1.8 TSI Coolant Level

Hi all, I'm new to this forum so I apologise if I am covering old ground with this but I have a question about the coolant level in my 2010 Octavia Scout.

I have only had the car around 3 months so I am still getting used to it but I have been monitoring levels closely (maybe too closely due to a bad experience with Seat Freetrack) and I have noticed a very gradual drop in the coolant level - in 5 weeks I have had to top it up with 50ml of water as it had dropped and looked like it was getting closer to the Minimum Mark although it has never dropped to or below that mark.

I cannot see any obvious leak (although hard to tell at the mo as its always so bloody wet!) - the car seems to be running fine and I have had no other problems with it since I got it so do I need to worry about having to top it up or is it an acceptable usage/loss and I'm just being too sensitive?

Thanks in advance

Dan.