Quote Originally Posted by Photo Engineer View Post
Distillation removes all inorganics and destroys or removes many organics. Particulate matter is left behind. From a volume distiller DW is easy to make and can be quite inexpensive.

Deionized water is made by running water through a mixed bed ion exchange resin which can be quite slow and quite expensive when compared to distillation.

The resin, once used, must be either discarded or regenerated, but a still can be kept operational for weeks or months at a time. They do need cleaning every once in a while to remove mineral scale.

For high end use, DI DW is used for ultimate purity. We at EK only used this for emulsion making in the most critical instances. DW was used to mix some solutions and tap water was used for things that were not sensitive to calcium or heavy metals.

Hi PE,
I am sorry but I have to respectfully disagree with you. I understand you background, but having worked in the analytical industry and working with equipment that looked for levels of inorganics(metals including sodium,calcium,etc,etc)down to ppt levels, distillation will not remove all inorganics. Boiling will not remove all insoluble salts etc.
You need to either use reverse osmosis or ion exchange cartridges to remove them.Now I am sure that for the levels photography would be bothered about, distillation would be more then good enough.
In the UK, things like DW are not so easy for 'joe public' to get now. It is thought that you must be making bombs if you want anything 'chemistry like' at all!!
BUT I am not wanting to get into a discussion as which method is better. For photography, I would settle for some DW. In the UK a lot of labs went over to DI rather then DW because of allsorts of problems from owning a still and inspections etc. It was just easier to buy bulk from people like BDH.