Hoping for some wisdom on how to go about investigating a water leak (I have no plumbing experience whatsoever) Have lived in this property for nearly 5 years. A few weeks ago, I noticed a small pool of water forming on the floor tiles at the side of shower door (as I have tried to demonstrate with a section of toilet roll in image 01 and 02. I looked at the seal around the shower tray and it seemed to be intact, nevertheless I had a plumber (from check a trade) come and assess. He advised me to replace the seal as it had not been changed during my stay at the property. I did as he suggested. Another couple of weeks go by and I notice what feels like 'sponginess' when stepping on the bathroom tiles and also noticed that the tile grout was darker and cracked in places (images 03, 04 and 05 - the lattermost probably best demonstrates this). At this point I stopped using the shower altogether out of fear of a major leak. I then investigated what was behind the shower head and the wall mounted shower mixer tap. All the pipes are sealed behind tiles. The shower backs on the store room which contains the water heater. There are some pipes that run from the water heater directly into the wall where the shower/mixer tap back on to (not sure what each of these pipes are doing exactly). Taking a closer look, the wall around the white pipe is friable and looks as though it was been leaking at some point, but the wall and the floor underneath was all dry to the touch. (Images 06 to 10) I have tried filling up 8 buckets (10litres) and pouring directly down the shower drain (no grout darkness reproduced) and following that tried the same pouring all over the shower tray seal (no grout darkness reproduced) As a newbie, I'm not sure where to begin. Do I try and break open the plaster board in the store room around the pipes coming from the water heater, or, do I try an remove the shower tray to see if the leak if coming from drain?