hardness mainly refers to the content of calcium and magnesium ions in the water. Hardness is divided into carbonate hardness and non-carbonate hardness. Carbonate hardness is mainly formed by calcium and magnesium bicarbonate, and it can also contain a small amount of carbonate, which can be precipitated and removed by heating and boiling, which is also called temporary hardness. After we usually boil water, the white precipitate in the container is this type of carbonate. Non-carbonate hardness is formed by calcium and magnesium sulfates or chlorides and cannot be removed by heating and boiling. It is also called permanent hardness.The sum of carbonate hardness and non-carbonate hardness is called total hardness. The calcium and magnesium ions in the water
only come from the dissolution of calcium and magnesium salts in the soil and rocks. When the water contains more carbon dioxide, it can promote the dissolution of calcium and magnesium. The hardness of source water varies greatly from place to place, the lowest can be several milligrams per liter, and the highest can reach several thousand milligrams. It is generally believed that the hardness of water plays a good role in maintaining the body's calcium and magnesium balance. But too high hardness also has an adverse effect on the body: after people are used to drinking soft water, they switch to water with too high hardness, and gastrointestinal dysfunction may occur at the beginning, affecting digestion and absorption. But generally it can adapt in a short time. In hard water cooking, calcium and magnesium are combined with protein, making meat and beans difficult to boil, and affecting digestion and absorption. Too high hardness not only consumes soap, produces scale, corrodes container equipment, but also affects the taste of water and even gastrointestinal function. The standard limit is 450 mg/L.