Hardness 09 : A water-quality indication of the concentration of alkaline salts in water, mainly calcium and magnesium. If the water you use is "hard" then more soap, detergent or shampoo is necessary to raise a lather.
US Department of the Interior, US Geological Survey USGS, Water Science Glossary of Terms, http://ga.water.usgs.gov/edu/dictionary.html (Some of this information is courtesy of the Nevada Division of Water Resources - the detailed water glossary at VA, USA 2009. http://water.nv.gov/programs/planning/dictionary/) , (ND/ Flood - Amer) {491}