Style chooser

Hi,

The water level in the radiator keeps on falling everytime I come back from a ride and each time before taking it for a drive I need to fill up the water.
The interesting part is the water level in the spare tank for the radiator keeps going up (as I would always check the water level in the spare tank is at the maximum mark and not topped all the way before taking the car out). Is this due to a problematic water pump?
I have recently (2 months ago) taken the car for a radiator...