QUOTE(danny~k @ Jul 30 2010, 10:37 )

A good way to find out is stick some tape in line with the water level and check it 24hrs later if its condensation it'll not drop a very noticeable amount. If its leaking you notice it. One thing any chance you might of splashed water over the back and not noticed while doing water change?
I had thought that but then I felt the carpet an its soaked so it couldnt be.. ive noticed water sitting under the front edge of the lid before but never the back or that amount.. ill try the tape test and measure the amount lost.. cheers