An all weather outdoor shower is easily done by locating the mixing valve inside the house and use a coupling shaft to locate the handle on the outside. You must use a standard tub type lower faucet (with the pull up to activate the shower) to allow the system to drain out when the shower is done. You also have to make sure everything slopes in direction of the water flow. We live in Bancroft Ontario so winters are well below freezing and we have been showering outside for 3 winters. Only issue we have is the shower head will freeze so we typically remove it after a shower or shower without it on when really cold. The system has worked well and it helps that nothing special needs to be done by anyone. no inside valves to close etc. Just turn off tap and everything drains.

Your concrete specialist will have ways of sealing/coating the concrete in a low-slip/textured finish. This can be done by texturing the concrete while wet and by using a textured epoxy with low-slip properties. Ask your concrete specialist what they recommend when used in a wet environment such as a shower.

Yes the windows are in place and I’m sorry I didn’t see this before we had to make some decisions

I am trying to source (in New Zealand) a shower tray which will fit into my alcove Sized 1900x1000 for the shower. Thus far for that size (and I have searched online and in merchants) found only tiled over solution to completely cover floor space. Not totally happy to have this as feel that tiles will be slippery when wet. Whereas have found smaller acrylic trays that are described as non slip even tho they are smooth. Can anyone suggest a supplier that they have used for trays and hinged/pivot doors of the size I require? Or if place a shorter acrylic tray to the length (probably 1200mm) of the glass wall, as will create a walkin with what do I cover the remaining 700mm of the alcove floor? The bathroom floor will not be any kind of tile, more likely to be a textured vinyl plank.