If dry, I'd say stained. But, what caused it in the first place? You mentioned a socket full of water - was the source of that found?
I wasnt sure if it was caused by a blocked gutter, in the original photo (https://i.ibb.co/K2nj0PS/brickorig.png) you can see a dip above where the water may have possibly overflowed when blocked?
Is there anything I can try to try and remove the stain from brick if it is this? Im worried if I try to sell in future that people are going to quetion the stain/mark as I certaintly would as a postential buyer.