I use filtered rainwater collected from the roof of the covered terrace which is polycarbonate and plastic guttering.
Or I use de-mineralised (not de-ionised) water.
There were volumes written on forums about this subject concerning types of water and the reaction with brass and soldered joints.
Geoff was even scrutinising the contents of a bottle of drinking water in the restaurant to see if it was suitable for his locomotive.
Just a bit more about steam locos and Regner in particular.
You saw 4 Regners at railexpo in steam:
My Chiemseebahn, not really for a novice and then 3 'Emmas'.
My old original one which is very easy to operate and maintain.
Pat and Gilles red 'old version' which ran well.
These locomotives are well run-in and behave differently to a virgin locomotive as the new version Emma I built for Jean-Claude.
First, the regulator servo ceased to function, bad luck/faulty product and nothing to do with Regner.
Then the gas jet blocked which I found home here was caused by a tiny fragment of PTFE tape.
Then it threw a crank because (and after advising Jean Claude to check regularly
) I failed to check tighten myself before running!
But despite these 'problems' The Emma is in my opinion good choice for a second locomotive or a 'faux débutant', semi beginner to steam.
Unfortunately the operation of steam locomotives can be a bit scary to start with and can even result in damage or injury.
It is fair to say that Roundhouse locos in my experience are the easiest and safest to operate.
That doesn't mean the others are dangerous but they require a little more attention and care.
Jean-Claude's novice friend also had a new Emma but built by Regner. Sadly on its first firing it almost blew up because the burner was incorrectly operated with the flame burning out of control in the smokebox.
That's not really a fault with Regner who at one time wouldn't sell a locomotive by post. He insisted on you collecting the machine from Germany after a period of practice on his layout.
This overburning can happen too with Accucraft locos which can also spit oil and water everywhere until the cylinders are warm.
The best thing is as you did in Paris was to practice lighting and operating few times someone else's
Maybe we should do our own tips and tricks for live steam operation.