Wang, MHS and Wang, LK (2022). Calcium and magnesium control technologies and terminologies. In: “Evolutionary Progress in Science, Technology, Engineering, Arts and Mathematics (STEAM)”, Wang, LK and Tsao, HP (eds.), 4 (10B), STEAM-VOL4-NUM10B-OCT2022. 39 pages. October 2022, Lenox Institute Press, Massachusetts, USA. https://doi.org/10.17613/py80-q048 ….. ABSTRACT: The coverage of this publication includes: (a) the environmental engineering significance, sources, types, and domestic/industrial/agricultural maximum levels of water hardness; (b) innovative dissolved air flotation softening processes and new chemicals for hardness removal; and (c) the related engineering terminologies and technologies. Special emphasis is placed on introduction of the unit processes and applications of innovative dissolved air flotation (DAF) softening processes and the new chemical combinations (lime, sodium aluminum and carbon dioxide). The innovative softening process systems introduced by the authors can be: (a) continuous DAF softening systems; (b) DAF sequencing batch reactor (SBR) softening systems; and (c) sedimentation-SBR softening systems. The authors are providing many opportunities for further research in the academic area of water purification.