quick question

i didnt loose weight this week and i was wondering if this could be water weight because a few days ago i got knocked down some stairs n got bruises all over me n im stiff everywere.

Um, possibly, but what does falling down stairs have to do with water weight?

i dunno :)  i dont really know much about water weight but i know you body retains water when you work out and it feels like ive worked out but over did it.

If you don't lose weight for a week it's usually just your body adjusting.  Bodies retain fluids when they're dehyrated, not when they're bruised.   Carry on with your normal, healthy diet, watch the portions, be as active as you can, drink plenty of fluids and see what the scales say next week.