

Pretty much. Brick is pretty good for load bearing so 50kg of water is not insane with the right hardware. Some anchors I’ve used were rated to do that with one screw, though I wouldn’t. I read your previous part as hanging from or inside of the ceiling but wall mounting should be good.
As for using heaters at all, it might not be purpose built, but it’s hard to beat free, even if they might have some quirks. The trick will be getting pressure moving in the right ways at the right time. The line coming from outside should give enough air to let water flow down easily to the cistern as long as you keep out contaminants/wildlife. A first flush and mesh should be able to manage that. And while I haven’t worked with ones like the top pair, ones like the bottom image, in grey, usually have a port at the bottom for draining/cleaning and you could cap off the cold water port, meaning you wouldn’t have to make extra holes. The hot water outlet port is usually at the top of the inner tank so it’d be fine.
The one thing I’m spotting is to remember the supply line has pressure and a very large supply, so you will have to make sure to either have a one way flow check valve or some other measure to keep it from sending water back up toward your rainwater inlet when using the piped supply or you could end up with a new pool where you don’t want it. Otherwise, very cool idea.





















Could you give me a minute to think it over? Oh, wait, shit…