The present invention relates to compositions and methods employing a wat er soluble magnesium compound. In certain embodiments, the composition inclu des water and water soluble magnesium compound, but lacks other materials co mmonly used in cleaning compositions. The methods and compositions can provi de magnesium ion at predefined ratios to calcium ion in water, such as magne sium ion in a molar amount equal to or in excess over a molar amount of calc ium ion. A water soluble magnesium salt including an anion of a water solubl e calcium salt is more effective than a magnesium salt with an anion of a wa ter insoluble calcium salt. These compositions can be used for reducing lime scale or precipitate formation from hard water, removing soap scum, or the like.