Hmm, the water, though cheap and passed through an RO unit, is not good enough. It will need a run through a DI unit to be of any good.
OTT do a little "domestic" one for £25, might give that a go.
(The thing said it would be <10ppm, obviously this isnt good enough)
It might be that they havent replaced the membranes though, but as I don't have a TDS meter I cant be sure.
I'll let you know what progress I make.
Phil