A waiter in the United States state of Texas was tipped US$500 (S$673) after serving a customer who ordered a bottle of water that cost 37 US cents, according to media reports.

The windfall for Mr Kasey Simmons, 32, who works at an Applebee's in Dallas, was the most surprising tip of his life - but it was not without a reason.

It was left by a woman as a reward for Mr Simmons' graciousness a day earlier towards her mother, who was having a hard time on the third anniversary of her husband's death, reported news station CNN.

Mr Simmons had met the older woman at a grocery store, and she was obviously depressed. He lifted her spirits by consoling her, and also paid for her groceries.

"On one of the most depressing days of the year ... you made my mother's day wonderful," CNN quoted the woman's daughter as saying on a note written on a napkin next to the tip. "You insisted on paying. Told her she is a very beautiful woman. I have not seen this woman smile this much since dad died."

Mr Simmons, who was almost in tears as he read the note, was quoted by CNN as saying: "It was only $17, but it's not about the money... It's about showing someone you care."

Unfortunately, he does not know the name of the woman he consoled that day. However, he does know that he made a difference in her life.