Question

why soft water give lather with soap and hard water didn't​

Answer 1

Because soft water has few calcium ions, there is noinhibition of the lathering action of soaps and no soap scum is formed in normal washing. ... Water that is not soft is referred to as hard water. In the UK, water isregarded as soft if the hardness is less than 50 mg/l of calcium carbonate.

Answer 2

Soap forms lather in soft water but not in hard water because hard water contains calcium and magnesium ions which react with soap to form a sticky white precipitate called scum.

Hope this helps you