Lebanese Slang: Literally means: "Hit the water, (it will still be) water" and metaphorically means, "it is useless to try and change some things", this expression is mostly used in a context where you ask someone to do something in a very specific way and take the time to explain, but they end up doing it the wrong way.  It's as if you had tried to "hit the water" (i.e. explained a very specific way of doing something), but it still turned out to be "water" (it was useless explaining, the job was done wrong).

Sample Conversation:

Person 1: Man, you have to write your name and sign every paper, (insistingly) at the bottom of the page!

Person 2: okay, got it.

Person 1 (30 minutes later): Man, i told you, you had to sign the bottom of each page, not the top of it.  100 pages to be signed all over again!  (exhales) di2 el may may ..(دق المي مي).