Gerolsteiner, hard G or Soft?

I’m just curious if the mineral water is pronounced with a hard G or Soft in Germany.

the same ‘g’ you use in green.

I assume that by ‘hard g’ you mean the sound as in ‘go’ and by ‘soft g’ the sound as in ‘Gerald’ (IPA [g] and [dʒ] respectively). Gerolsteiner is pronounced with a [g] sound. Offhand I can’t think of any instance where a word-initial ‘g’ is pronounced [dʒ] in a German word.
Didn’t know they were marketing their bubbly water internationally.

ooooo sulphur water =) makes me remember water at our summer cottage - serious sulphur content.

I think you can get it at, I know they carry it in the main exchange at the sub base in New London occasionally.

I don’t know one either - the [dʒ] sound does not occur in German words except a few of recent foreign origin (such as Dschungel - from English jungle, originally from Indian languages). That [dʒ] needs to be rendered phonetically as dsch is a clue that it is non-native in German. I don’t think you can go far wrong in pronouncing every g in German as [g] - except for words of Italian origin; these are pronounced on Italian rules i.e. g before i or e is [dʒ]