Low antifreeze warning light keeps coming on

Hi all,
Every few days I have to add water to the antifreeze reservoir. This has been going on for several weeks. No leaks can be found and no evidence of water in the oil. Any ideas on where the antifreeze is going?
2006 VW Jetta TDI
193,xxx miles

the water pump can leak,its a difficult one too see if the undertray is still in place!!,remove it and look fron underneath you should see a leak/stain around the crank area. hope this helps.billy.

If you have a radiator pressure tester you can apply pressure to the system and look for leaks.
I used one on another vehicle with a small coolant leak that I could never find until I applied pressure to it...

Most automotive parts store carry them, and some will rent them out.

https://www.harborfreight.com/radiator-pressure-tester-kit-63862.html

This is what you need to replace:
https://www.idparts.com/coolant-flange-for-cylinder-head-seal-a5-brm-p-5526.html
The coolant flange is located in front of the engine, easy 20 minuets job.

coolant leakage

I have it too and think it's the pump. i will change this summer when I replace the timing belt parts. For now I loosened the cap on the reservior, which slowed the leak. I did replace the thermostat and housing about a year ago, so it's probably not that. I need to add some every 2 to 3 months, which I do.