Well, hard water means it could be Ca+2 or Mg+2 ions, but it doesn’t have to be. Any metal or mineral in a “high” concentration (often as a dissolved salt) would make water hard. e.g. Salt water is hard compared to tap standards.

The water for the above user certainly could have been corrosive, or an allergic reaction could be the explanation. With a rural, rock ravine environment, any number of minerals could be in the water. You’re also more likely to get other contaminants like toxins in water not properly tested and treated.