9. References:

A. Ryznar, John W.; Langelier, W. F. (April 1944). "A New Index for Determining Amount of Calcium Carbonate Scale Formed by a Water".
B. Langelier, W. F. (October 1936). "The Analytical Control of Anti-Corrosion Water Treatment". Journal of the American Water Works Association. 28 (10): 1500–1521.
C. "Map showing the rate of hardness in mg/L as Calcium carbonate in England and Wales" (PDF). DEFRA/ Drinking Water Inspectorate. 2009.