Can you use soaps and synthetic detergents to check the hardness of water?

Explanation

Soaps can be used to check the hardness of water as a sample of soft water will form lather with soap immediately but hard water will form lather only after precipitation of all the `Ca^(2+)` and `Mg^(2+)` ions as calcium and magnesium soaps respectively. Synthetic detergents cannot be used for this purpose as they produce lather with soft as well as hard water.