I have water problems with my Golf IV 1.6 (2002)

there has to be a leak somewhere .i would go to a radiator service centre and ask for a pressure testto be done. that will tell whether there is aleak and if it is internal.it only takes acouple of minutes,and it takes a lot of the guess work out of it .who knows it may be as simple as the thermostat sticking and forceing a bit of water out the overflow , get the pressure test first and then you will know what to do