A glass of water

A young man doesn't know if he should get married or not. His friend advises him to get married:
- At least when you are old there will be a person who will bring you a glass of water.
And the young man decided to get married.
50 years later they meet again. The friend says:
- Remember, I advised you to get married: now you have someone who can bring you a glass of water, don't you?
- Yes, I do. You were right. The problem is - I'm not thirsty at all.