The bartender said, "Well, since it's your birthday, this one's on me."

As the lady finished her drink, a woman, to her right, said, "I'd like
to buy you a drink, too."

The lady said, "Thank you, how sweet of you.  Ok, then bartender,
I want another scotch, with two drops of water."

"Coming up," said the bartender. 

As she finished that drink, a man, to her left, said, "I'd like to buy
you a drink too." The lady said, "Thank you very much, my dear. 
Bartender, I'll have another Scotch, with two drops of water."

"Coming right up," the bartender said. As he gave her the drink,
this time, he said, "Ma'am, I'm dying of curiosity. Why the scotch
with only two drops of water?"

The old woman giggled, and replied, "Sonny, when you're my age,
you've learned how to hold your liquor.  Water, however, is a whole
other issue."