What is hard water and soft water in dyeing?

Water is divided into soft water and hard water. Water that does not contain or contains a small amount of calcium and magnesium ions is called soft water, and vice versa is called hard water. The hardness component of water, if it is caused by sodium bicarbonate or magnesium bicarbonate, is temporary hard water (boiling temporary hard water, decomposed sodium bicarbonate, and the formed insoluble carbonate precipitates, and the water changes from hard water to soft water) ; If it is caused by sulfate or chloride containing calcium and magnesium, it is permanent hard water and cannot be removed after boiling. The above two kinds of hardness are collectively called the total hardness. Roughly divided according to the total hardness value of water, 0-30ppm total hardness is called soft water, total hardness above 60ppm is called hard water, high-quality drinking water does not exceed 25ppm, and high-quality soft water has a total hardness below 10ppm. In natural water, unpolluted rainwater and snow water away from cities are soft water; spring water, stream water, river water, and reservoir water are mostly temporary hard water, and part of groundwater is high hardness water.

When water droplets condense in the atmosphere, they dissolve carbon dioxide in the air to form carbonic acid. Carbonic acid eventually falls on the ground with rainwater, and then penetrates the soil to reach the rock layer, dissolving lime (calcium carbonate and magnesium carbonate) to produce temporary hard water. Caves and hard water near the caves in some areas are formed in this way.