As a noun phrase, the infinitive verb 'to drink' expresses an non-actualized event. That is, the assumption is that neither the speaker/writer nor the listener/reader has actually drunk water as a solution for the situation they're discussing.Originally Posted by Darlene
The gerund 'Drinking' as a noun phrase expresses an actualized event. The assumption is that the speaker/writer has drunk water as a solution for the situation they're discussing, or knows someone that has, and so the speaker/writer is passing on that information based on personal experience or knowledge.
In short, both 1. and 2. sound natural. The situation will determine which is best.
As for 3., "It" is an expletive, or dummy subject. It has no meaning. The real subject of the sentence is underlined below.
It's a good idea to drink water.
To drink water is a good idea.
TO tells us the speaker/writer hasn't experienced the event, so 3. is the same as 1. But sentences that begin with expletive "It" serve to disquise the true subject, and in doing so, hide the fact that the speaker/writer hasn't actually experienced the event, but makes them sound as if they have. People tend to adopt the advice of those who have experienced the event, so by using expletive "It" the speaker can appear as if s/he has experienced the advice, when in actuallity (TO) s/he hasn't done that.
In sum, all three of your examples sound natural, and they express different things: ING expresses an actualized event, whereas TO expresses a non-actualized event. Sentences that start with expletive "It" disguise the subject, and for a very good reason: It makes the speaker/writer appear as if s/he has experienced the event, or knows what s/he is talking about.