Not hold water - used in order to say that plan, argument or idea is not true or does not work

e.g. The notion that Douglas Home was lazy just doesn't hold water; when he was Prime Minister he was up and working by 6.30 every morning. In/into hot water - in trouble with people in authority because of something you have said or done.

E.g. This is not the first time that Durenberger has been in hot water with the Senate Ethics Committee.

Smth is like water off a duck's back - used in order to say that advice, warnings, rude remarks etc. have no effect on someone. e.g. No matter how hard he tried, he could not upset Branson, his subtle rudeness and game-plying tactics were like water off a duck's back.

A lot of water has gone/ passed/ flowed under the bridge - used in order to say that a lot of time has passed or that a situation has changed a lot since a particular event.

E.g. A lot of water has flowed under the bridge since we won the trophy; it will be interesting to see what has been happening to the members of the team.

Pour cold water on smth - to say that you do not think an idea or plan is good or sensible, so that people stop using it or being interested in it.

e.g. To make matters worse, China's allies poured cold water on its plans for industrial expansion.

Test the water/waters - to find out what reaction people have to a plan or idea, before you begin to use it.