Quote Originally Posted by Ian Grant View Post
The only distilled water you can truly
trust is de-ionised prior to distillation.

However in practice in this day and
age de-ionised water is all you need for
photographic purposes. Ian
De-ionization deals only with contaminants of an
ionic nature and yields ionic free water. The usual water
softening by ion-exchange yields soft water with lots of ions.
Reverse Osmosis types can reduce considerably both ionic and
non-ionic contaminants. Distilled water is essentially de-ionised
de-mineralized water.

As for ultra-pure, fractional distillation, and ???. As for myself
and very hard water a small capacity RO unit may do. They
cost little but do need to be plumbed in. Dan