Soft water

Soft water is water with a very low mineral content. The opposite is hard water, which has a high mineral content. Around 15% of the United States' water supply is soft water. 

Soft water contains less than 17 parts per million of calcium and magnesium.  This means the concentration of minerals in the water is very low.  

 Sources 
Most soft water comes from peat or igneous rock sources, such as granite. However, some comes from sandstone sources, since those sedimentary rocks are usually low in calcium and magnesium. 

 Advantages & disadvantages 
Hard water may be better for the heart than soft water. Its calcium (Ca) and magnesium (Mg) ions may be a dietary supplement for some people. 

The main disadvantage of hard water is it deposits calcium carbonate on pipes, especially hot water pipes. (This is called "scale formation".) The deposits can block pipes and reduce boiler efficiency. 

Also, soap and detergents work less well in hard water. These effects increase as the hardness of the water increases.Section 36 "Hardness" https://www.epa.ie/pubs/advice/water/quality/Water_Quality.pdf  Meanwhile, soft water lathers easily with soap.

 References 

Category:Water