A Scotch with two drops of water

A lady goes to the bar on a cruise ship and orders a Scotch with two drops of water. As the bartender gives her the drink she says, 'I'm on this 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 that drink, the man to her left says, 'I would like to buy you one, too.' The old woman says, 'Thank you. Bartender, I want another Scotch with two drops of water.' 'Coming 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've learned how to hold your liquor. Holding your water, however, is a whole other issue.'