water. Soft water is less likely to scum with soap, while hard water is the opposite. Natural soft water generally refers to river water, river water, lake (freshwater lake) water. Hard water treated by softening refers to softened water obtained after the calcium and magnesium salt content is reduced to
1.0 to 50
mg/liter. Although boiling can change temporarily hard water into soft water, it is extremely uneconomical to use this method to treat large quantities of water in industry.
In our daily lives, we often see the kettle with a long time after the inner wall of the scale will be generated, this is because we take the water contains a lot of inorganic salts, such as calcium, magnesium salts, etc.. These salts in the water at room temperature can not be found with the naked eye, once they are heated and boiled, there are a lot of calcium and magnesium salts in the form of carbonate precipitation, they are close to the wall of the kettle to form limescale. We usually put the content of calcium and magnesium ions in water with "hardness" as an indicator to indicate. Hardness of 1 degree is equivalent to 10 mg of calcium oxide per liter of water. Water below 8 degrees is called soft water, above 17 degrees is called hard water, between 8 to 17 degrees is called medium hard water. Rain, snow water, rivers, streams and lakes are soft water, and spring water, deep well water and sea water are hard water.
Some of the calcium and magnesium ion content is very high in the water but do not see scale generation, this is because these calcium and magnesium ions in the form of chloride salts, they are soluble, so when heated and can not be precipitated out.
The hardness of water has a great impact on daily life. Such as water hardness when washing clothes do not foam; living in a foreign country because of the hardness of drinking water is not adapted to the symptoms of soil and water; pot limescale will make the pot's thermal conductivity decline; industrial boiler limescale can cause an explosion. Therefore, living and industrial water should be appropriate control of water hardness. Often drink soft water (pure water) easy to get cardiovascular disease, often drink hard water (mineral water) easy to get kidney stones.