Possible Clues:

• Pipe clogger, at times
• Cause of mineral buildup in faucets
• Cause of limescale
• H to O that's difficult, it seems
• Some ice, perhaps, if there's lime in it
• Might 23 down make fur?
• It doesn't lather easily
• You get it with lime and ice
• 15 across?
• Perhaps it's ice that may have one furred up