Water hardness causes white mineral buildup in homes

White stains on household surfaces, such as shower glass, faucets, and glassware, are often caused by water hardness. This phenomenon occurs when water contains high concentrations of minerals, specifically calcium and magnesium.

As water travels through soil and rocks, it dissolves minerals that are then carried into aquifers and distribution systems. The level of hardness is determined by local geology and water treatment processes. According to the U.S. Geological Survey, water is classified based on its calcium carbonate (CaCO₃) equivalent concentration: soft (up to 60 mg/L), moderately hard (61–120 mg/L), hard (121–180 mg/L), and very hard (above 180 mg/L).