Why does hard water not from lather with soap ?

Explanation

Hard water contains bicarbonates , chlorides and sulphates of `Ca^(2+)` and `Mg^(2+)` . These combine with soap molecules to form precipiatates of calcium and magnesium salts of soaps.
`underset("(Soap)")underset("Sod. Stearate")(2C_(17)H_(35)COONa)+Ca^(+) to underset("(Curdy white ppt.)")underset("Cal. stearate")((C_(17)H_(35)COO)_(2)Ca)+ 2Na^(+)`
`underset("(Soap)")underset("Sod. Stearate")(2C_(17)H_(35)COONa)+Mg^(2+) to underset("(Curdy white ppt.)")underset("Mag. stearate")((C_(17)H_(35)COO)_(2)Mg)+2Na^(+)`
As a result , soap is wasted and hence hard water does not produce lather with soap.