"Water" joke

A senior woman is on a cruise ship and wanders up to the bar and asks for a
scotch with two drops of water. As the bartender gives her the drink she says,
"I'm on the cruise to celebrate my 80th birthday and it's today."
The bartender says "Well, since it's your birthday, I'll buy you a drink.
In fact, this one is on me."
As the woman finishes her drink, the woman to her right says, "I would
like to buy you a drink too."
The old woman says, "Thank you. Bartender, I want a scotch with two
drops of water."
"Coming up," says the bartender.
As she finishes her drink, the man to her left says, "I would like to buy
you one too.
The old women says, "Thank you. Bartender, I would like another scotch with
two drops of water."
"Comin' right up," the bartender says. As he gives her the drink he says,
"Ma'am, I'm dying of curiosity. Why the Scotch with only two drops of water?"
The! old woman replies, "Sonny, when you're my age, you learn how
to hold your liquor. Water, however, is a whole other issue."