I don't think there's any idiom here, it means only what it literally says: the water is flowing out of me. Perhaps I am some kind of water spirit and water flowing out of me is totally normal. Who knows.
It could conceivably be spoken by someone who is just about to give birth. (Although there is a more clinical term magzatvíz for that kind of water.)
Or it could be just coming out of my clothes. :)
There is water on the floor, how did it get there? Oh, it is coming out of me, from my clothes, from my shoes, from my shopping bag.... oops.