i really wouldnt try it. I had a steam generator iron and it said don't use anything other than tapwater in it, but I ignored it and thought it would help as we have very hard water and used my filter jug water.....
I broke the iron and it also started fizzing and dripping out the water instead of steam and the water was brown and stained so many of my clothes. I since found out that the minerals left in the water after filtration turn brown in these kind of appliances.
Not what you want in an expensive ironing appliance. I don't have the spare case for another steam generator at the moment, so have had to bridge the gap with a regular iron which is really rubbish in comparison to what I had.
Moral of the tale: Always follow makers instructions......