i'm at the sewer water thing rn and it's pitch black and my flashight doesn't work
Thanks for the comment. You don't have flashlight after you get captured. If you read the text when pressing F key, it says that you don't have it.
As far as it goes for the sewers, you are supposed to pick up flares, which are next to you. It's not completely dark and there is also text indication, if you pay attention to it.