There should be a small hole in the nob that allows a small straight shank item to turn it to unlock. If not your only choice is to try to remove the jam and use a butter knife or something slim to get the foot of the knob moved.
You have time to post on the internet that you locked yourself out of a bathroom with the water running , to ask for help on how to get in, then 10 minutes later realize to turn the water off?
You have to be fucking with us.........
I smell something fishy.