Hard water is water that has high mineral content. It contains minerals like limestone, chalk or gypsum. Hard water contains calcium and magnesium ions. These ions convert sodium or potassium soap into hard water into insoluble calcium and magnesium soap, respectively. These insoluble soaps are separated from the water like Scum and are useless for the purpose of purification reagent. Due to this viscous substance in clothes washed with hard water and soap, the dye is not absorbed evenly.