is there anything in the U.S. that is comparable in terms of mineral content?
Piwniczanka is a hydrogencarbonate natural water with mostly calcium, natrium, magnesium ions.
Mineral waters in US and many European countries (including Poland) are frequently achieved by cleaning ordinary water in osmotic proces to pure H2O and artificial mineralization. Not like in commercials. And not like traditional Kryniczanka and Piwniczanka which are obtained from commonly known sources. May be you can't find a strict equivalent in US, but you can try to find sth. having similar composition.
You should look for sth. similar to Piwniczanka composition:
Cations
calcium Ca2+ 181
sodium Na+ 115
magnesium Mg2+ 92
potassium K+ 13,6
lithium Li+ 0,5
Anions
hydrogencarbonate HCO3- 1255
sulphate SO42- 28,4
fluoride F- 0,23
So in Poland I learned to drink a few liters of Piwniczanka and other mineral water a day and I have never been this healthy in my life.
Don't overdo! Demineralization is a problem in Africa may be, but not in US or Europe. We already have all necessary minerals in our food. You can't ingest so many minerals with water without negative effects for you in the future. Piwniczanka has 1756 [mg/l] of mineral elements in total. It is pretty much! Natural and ordinary (tap) water should have below 500 [mg/l], mineral water should have above 1000 [mg/l].