Science, Tech, Math › Science What Hard Water Is and What It Does Share Flipboard Email Print Hard water is simply water that contains high levels of calcium and magnesium ions. Tim Graham/Getty Images Science Chemistry Chemical Laws Basics Molecules Periodic Table Projects & Experiments Scientific Method Biochemistry Physical Chemistry Medical Chemistry Chemistry In Everyday Life Famous Chemists Activities for Kids Abbreviations & Acronyms Biology Physics Geology Astronomy Weather & Climate By Anne Marie Helmenstine, Ph.D. Chemistry Expert Ph.D., Biomedical Sciences, University of Tennessee at Knoxville B.A., Physics and Mathematics, Hastings College Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels. our editorial process Facebook Facebook Twitter Twitter Anne Marie Helmenstine, Ph.D. Updated May 24, 2019 Hard water is water that contains high amounts of Ca2+ and/or Mg2+. Sometimes Mn2+ and other multivalent cations are included in the measure of hardness. Note water may contain minerals and yet not be considered hard, by this definition. Hard water occurs naturally under the condition where water percolates through calcium carbonates or magnesium carbonates, such as chalk or limestone. Evaluating How Hard Water Is According to the USGS, the hardness of water is determined based on the concentration of dissolved multivalent cations: soft water - 0 to 60 mg/L (milligrams per liter) as calcium carbonatemoderately hard water - 61 to 120 mg/Lhard water - 121 to 180 mg/Lvery hard water - more than 180 mg/L Hard Water Effects Both positive and negative effects of hard water are known: Hard water may offer health benefits as drinking water, compared with soft water. Drinking hard water and beverages made using hard water can contribute to dietary requirements for calcium and magnesium.Soap is a less effective cleaner in hard water. Hard water makes it harder to rinse soap, plus it forms a curd or soap scum. Detergent is also affected by the dissolved minerals in hard water, but not to the same extent as soap. More soap or detergent are required to clean clothes and other items using hard water compared with soft water. Hair washed in hard water may appear dull and feel stiff from residue. Clothes washed in hard water may develop a yellowish or gray discoloration and may feel stiff.Soap residue left on the skin from bathing in hard water can trap bacteria on the skin surface and disrupt the normal balance of microflora. Because the residue inhibits the ability of skin to return to its slightly acidic pH, irritation may occur.Hard water can leave behind water spots on dishes, windows, and other surfaces.Minerals in hard water can deposit in pipes and on surfaces forming scale. This can clog pipes over time and decrease water heater efficiency. One positive aspect of scale is that it forms a barrier between pipes and water, limiting leaching of solder and metals into the water.The electrolytes in hard water can lead to galvanic corrosion, which is when one metal corrodes when in contact with another metal in the presence of ions. Temporary and Permanent Hard Water Temporary hardness is characterized by dissolved bicarbonate minerals (calcium bicarbonate and magnesium bicarbonate) that yield calcium and magnesium cations (Ca2+, Mg2+) and carbonate and bicarbonate anions (CO32−, HCO3−). This type of water hardness may be reduced by adding calcium hydroxide to the water or by boiling it. Permanent hardness is generally associated with calcium sulfate and/or magnesium sulfates in the water, which will not precipitate when the water is boiled. Total permanent hardness is the sum of the calcium hardness plus the magnesium hardness. This type of hard water may be softened by using an ion exchange column or water softener.