there might be a big turn offy tap thing somewhere that will close down all your water when you don't need it?
ok i'm going to quit the baby talk. if you haven't already follow the offending pipe back and try and find something that will turn it off.
sometimes they obviously look like a tap, but sometimes aren't so big and look like this one and you need a screw driver or knife. you just turn it ninety degrees until the slot is across the direction of the pipe, instead of with it. (this one is open)
but you've probably tried this?