Qual é a diferença entre This is water to drink. e You are not one to talk. ?Podes indicar apenas respostas exemplo.

The first one is: This is (object) to (action).
It’s a instruction.

For example: This is water to wash your hands.

The second sentence however, is not an instruction.

“You are not one to (action)”= you do not to this action normally( from speakers perspective)

For example: in the sentence” You are not one to talk. Means that the speaker has noticed that the other person does not talk very much.

To put it simply:

First sentence: speakers instruction on a others action.

This is medicine to drink.
(Drink this medicine)

Second sentence: speakers observation on a others action.

You are not one to drink your medicine.

( You don’t ever drink your medicine)