The woman had spent just 30p on a bottle of water but tipped Kasey Simmons a life-changing amount of money.
A thank you note written on a napkin was left with the tip and explained it was a reward for an act of kindness carried out by Mr Simmons the day before.
Speaking on Facebook, 32-year-old said: "I felt undeserving of the tip being I gave them the most embarrassing service ever. It's almost like two people fighting over the bill at one of my tables, I would've argued that much of a tip if they were still there but they were not anywhere to be found.
So you win, I have your generosity in my heart and with your money I'm trying to multiply the love, just ask some of the employees at the very place this all started in a Kroger checkout line."
The waiter, who works at Applebee's restaurant in Dallas, USA had approached an elderly woman at his local Kroger supermarket the day before after seeing she looked depressed.
He paid $17 for her groceries and with smiles and jokes attempted to lift her spirits but he never expected anything in return.
As reported by CNN , the note and tip was from the woman's daughter, thanking Mr Simmons for his kindness.
"On one of the most depressing days of the year ... you made my mother's day wonderful," the note said.
"You insisted on paying. Told her she is a very beautiful woman. I have not seen this woman smile this much since dad died."
The daughter did not reveal her or her mother's name but Simmons' kindness made a difference, and the daughter wanted to let him know.