Good question because the quality of destilled water can vary enormously. But this is the same with R.O. water. I am using Brita (TM) water which is enough filtered to get rid of all regular problems in photography and it is very suitable for use of "photo" water. One Maxtra filter can do about 80 ltrs. and it costs about Eur. 4,00. About Eur. 0,05 / ltr. and always available. The end quality also depends of the type of input water but here in Holland it is pretty good. In Ukraine it sometimes is a problem in a high amount of iron (rusty tubes).