I think it is hard water.But my doubt is even if we add more surfactant to hard water there will be no use because soap doesn't dissolve.then what is its use....
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It depends on the type of surfactant. There are basically four types of surfactants: anionic, cationic, amphoteric and nonionic.
Anionic surfactants are probably the most common in everyday products (laundry powder, dish wash, shampoo etc.) because they are cheap and effective. By these types has the disadvantage that they will bind with the calcium-ions present in hard water, and thus loose their surfactant properties. In the end they precipitate and settle as soap-stone in pipes or the washing machine.
The ways to overcome this problem is either to add more surfactant to ensure a surplus, or add some chealant/binder in the product that binds the calcium stronger than the surfactant. Or you can off course choose another type of surfactant that are less sensitive to hard water.
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$\begingroup$ No ! FrankS ! Anionic surfactants are not always reacting with Calcium ions to produce a precipitate in hard water. This reaction happens if the surfactant is the usual and well-known soap, produced by the action of soda on vegetable oils. This soap is made of oleate or other derivates from fatty acids, and it has the disadvantage that it binds with calcium in hard water, and settle as soap-stone in washing machines. But this only happens with soap. With modern anionic detergents, this disadvantage disappears. $\endgroup$– MauriceCommented Jul 14, 2020 at 16:18
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$\begingroup$ can you expalin the reason why carboxylate of soap have more affinity for cations than the sulfonates of detergents , it is also mentioned in wikepedia but i cant find the reason? $\endgroup$ Commented Jul 14, 2021 at 20:30
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$\begingroup$ Hi Samardeep. No, not in detail. Maybe it relates to solubilities of inorganic carbonates vs. sulfates? $\endgroup$– FrankSCommented Jul 16, 2021 at 8:41