What are the conversions for Water Hardness? Hardness is mostly expressed in ppm (mg/l as CaCO3) or in German degrees (°d). There are also other units used for the expression of hardness, and the conversions are presented below. Water Hardness Conversion Table×Water Hardness Conversion Table admin2020-02-17T10:06:01-07:00March 18th, 2015|Categories: Hardness, Water Quality|Comments Off on What are the conversions for Water Hardness? Share This Story, Choose Your Platform! FacebookXLinkedInPinterestEmail