Knjaz Milos is one of the the best high mineral waters I have had from Serbia. It has 10% of your DV of Na as well as 10% DV of Ca and 15% DV of Mg. This is one of my everyday water that is pretty easy to find in Astoria. This has a great taste and is a classic to light bubble. I think the new one I have been getting (green bottle) has a higher CO2 content than the classic one(blue bottle), but I can't confirm this and they have not responded to my inquiries.
Here is more info about the water from the site and more mineral facts:
Knjaz Miloš is one of the few mineral waters in the world with a very specific composition. The water is characterized by an ideal calcium to magnesium ratio (2:1), which allows optimal absorption in our bodies.
Knjaz Miloš is one of the oldest Serbian brands and is often the first thing that comes to mind when mentioning Serbia.A two century long tradition speaks in favor of the quality of Knjaz Miloš water, while the quality itself is greatly influenced by the fact that all of the springs are located within the undamaged ecosystem of the Aranđelovac spa.