As a duck takes to water means that you learnt very quickly or immediately and enjoyed the experience
This term refers to someone in a particularly vulnerable situation.
This is not an idiom I have ever heard. Perhaps you mean water cooler talk, which means chat that might occur between workers at the water cooler or anywhere else.
It takes a long time to do an important job
This is not an idiom. An idiom is an expression whose meaning cannot be deduced from its elements. To go through fire and water for someone is easily understood to mean to make a special effort and to undergo difficulties for that person's sake.
It is not an idiom, it is fact. A hose can be used for a water level with hundreds of feet between the two points. As long as two bodies of water are connected somehow, they will be at the same level. As an idiom, it would mean a person tends to seek out people they feel are equal or have the same point of view.
First, when you see the phrase AS ___ AS ___ it is A Simile instead of an idiom. It is easy to figure out the meaning of a simile. Water flows quickly, so the simile means that whatever it is, it's as fast as water flowing.
RFP is not an idiom. It's an abbreviation.
It's not really an idiom. It means "what are you thinking about."
It is not an idiom, it means your nose is itching.
idiom means expression like a page in a book
It's not an idiom. It means the tip of your nostril.
"Sieve" is not an idiom. See the related link.