well I didn't like the grout to be honest Jay. we used a Mapei grout but it was very sandy and coarse. Will have another go and the Silicon and then start a re-grout.
just a thought if you haven't grouted top of tiles to wall it might be condensation as MG said or it could be were your shower rose is fitted to wall if its on a bracket theres some dodgie ones out there you need to fill drill holes with Silicon before putting screw in
the only other thing i can suggest is get a large piece of plastic and some gaffer tape and tape it over the tiles up to rose height so no water gets on wall tiles and use see if it leaks if not lower it down the wall in stages till you pin point the leaking area i remember you weren't happy with grout might be it to
Water ingress should not be a problem providing the install, grouting and sealing is done correctly as any minimal transfer through grout is taken care of by osmosis.
Should you have a fail then that is what the tanking is for, preventing water from penitrating and damaging other areas of the property. (fails arnt always due to workmanship or install mistakes, buildings especially new ones move as they settle)
Tanking is not a water collection system it acts to prevent water getting to and damaging other parts of a property. Due to soil stack positioning for eg kitchens are often positioned below upstairs bathrooms so any leak could do a lot of damage especially to electrics. Installed correctly the physical off a roll systems create a tank so ensuring the safety of the rest of the building.
Nice to see so many high profile voices in one place
Just bumping some of the older popular (sometimes not so popular) threads. Probably wont be current discussion these days but I just need to do it. So just ignore the thread if it's not current for you.