“Hard water” sounds horrible, drinkable?
Water hardness actually refers to the concentration of calcium and magnesium ion in the water. There is more or less amount of calcium and magnesium ion in the natural raw water. These ion exist in the calcium bicarbonate or magnesium bicarbonate. When the water is boiled, the bicarbonate salt becomes carbonate and the insoluble carbonate will precipitate, looking whitish.
The carbonate content in the water (equal equivalence) can be used for the calculation of hardness. 1PPM is the hardness unit, and stands for 1mg/L of calcium carbonate. Generally speaking, if the hardness is more than 170PPM, the water is hard water, and if less than 80PPM, it is soft water. The recently published “Living Water Sanitary Standards” stipulates 450PPM as the standard of hard water.
However, not all hard water after boiling will precipitate limescale, for calcium and magnesium ion may exist in sulfate or chloride, and such water is permanent hard water in which the calcium and magnesium ion cannot be removed by daily means. The above-mentioned hard water caused by bicarbonate is temporary hard water.
Calcium and magnesium are the essential mineral of human body, but oversupply of mineral will cause problems, and so we need to calculate the possible intake of calcium and magnesium.
Beijing’s tap water has been notorious for its bad quality and high hardness. With its upper limit of 600mg/L as the calculation basis, if we drink 2 liter of water, the total intake of calcium and magnesium is less than 600mg. And this is on the assumption that the water is permanent hard water. For normal people, a daily intake of 1000mg of calcium and magnesium is acceptable.
Extract from China Technology Website