Question

how would you distinguish between hard water and soft water using a soap?​

Answer 1

in hard water soap is lost after applying water 2 it and no foam is formed

in soft water foam is formed

Answer 2

In the water where more lather is formed that is soft water and where less lather is formed that is hardwater

This is because in hard water most of the soap is used in reacting with the calcium and magnesium ions to form scum