bungie
Remove the shower rose, fit a pressure gauge to the outlet. Turn the water on, the off, If the gauge pressure drops the leak is in the pipework from the taps to the rose.
You have all ready tested the waste and tray finding it ok.
Check around the shower door, and all the grouting.
Run the shower and ensure the water is not running down the door onto the floor outside the tray and straight down the hob into the ceiling.
Gimmie a call if this is of no help
