The concentration of magnesium in natural bodies of water is second highest after the concentration of sodium. However, magnesium dominance is rarely seen in natural water. Fresh water is usually dominated by calcium, while in alkaline water sodium is the main element. In most water bodies, magnesium concentration falls between 1 mg/L to 40 mg/L. The calcium to magnesium ratio in natural water has a certain relationship. In water where the total dissolved solids (TSD) are less than 500mg/L, the ratio ranges from 4:1to 2:1. If the TSD increases further, the concentration of magnesium will exceed calcium by several times. Fresh water contains much more calcium than magnesium due to the abundant calcium in the earth’s crust. However, since the chloride and sulfate of magnesium has higher degree of hydrolysis than calcium does, in alkaline water, the magnesium content is higher than calcium.