son nim does not always mean a girl or woman. It is just a customer or guest of any sex. I put Mr. be careful the water is hot. they said Ms. be careful the water is hot was correct. The other time I put guest be careful the water is hot. They said "Miss be careful the water is hot."- was correct.
you obviously don't know english well enough to make a helpful comment. "'s" isn't ONLY for possessives; it's also for contractions. of course you wouldn't know that because your English is basic. you probably don't understand the difference between IT'S and ITS.
"the water's hot" is correct and should be reported.