Hi Ewen
We also live in a hard water area and after lodas of research, there is no cheap way to make pure water in anytype of quantity.
We did do conservatory roofs as per the above posting and most people were ok with it.
Recently we've gone over to using wfp along side traditional methods and the 2 work together brilliantly.
As we bought the system 'one bit at a time' we ened up to start just with the cheaper RO (filter), pump and water barrel. I think the whole lot was well under £200 from RO-Man:
http://www.ro-man.com/shop/product_info.php?cPath=22&products_id=30They also do a really good explanation page:
http://www.ro-man.com/ro-facts.htmlAll we did then was buy a few more barrels and with a hand pumped pressure container, clean conservatory roofs using that with a cheapo wfp brush seeing as we already had half a system.
Conservatory roofs went from being a bit of a pain to being a doodle with quite incredible results. Pure water does seem to clean staggeringly well and does do a better job than tap water.
As well as that, using a mop and squeegie with pure water, especially in a hard water area, w-o-w. What a difference.
Also, in a hard water area you can only use an RO system.
Cheers