[Hand15]

Well... until recently I thought they were just the same pure water..
But last week when I did my experiment on creating a collodal gold, the instructor insisted us using deionized water in the experiment and warned us not to use the distilled water.

So what's the difference? They are both purified water right?.

[Alpha-Omega]

Distilled water and deionized water are different...and there are so many different grades of purified water you could get lost in them.

There is distilled water, deionized water, doubly distilled water, purified water, HPLC Grade water, 18.2 megOhm water,...please read this link:

http://en.wikipedia.org/wiki/Distilled%5Fwater

Basically, distilled water is boiled water that has been purified of "all impurities."  The mineral and salt scale remains in the distillation apparatus.

Deionized water is purified water that has been assayed for salt and mineral content.

Edit:  TYPOS

[Gerard]

when i was still a research assistant in the fermentation engineering laboratory i was also warned not to use deionized water and to only to use distilled water when mixing the bacillus inoculum to form the mother solution...
i think in the biological aspects of chemistry deionized water is far more stronger in dissolving capacity than distilled water,whose components are soft ions of sulfate after the heavy ions of calcium and magnesium have been scaled by boiling

[Alpha-Omega]

You pick your grade of water based on your application:

IC requires the use of 18.2 MegaOhm water-this grade of water is distilled, deionized, degassed, run and rerun thru a reverse osmosis process.

For HPLC applications-mot are done using UV detection so HPLC grade water would be appropriate since it is assayed for organics which absorb in the UV range.  It would not be appropriate and is not appropriate for IC applications since it is not assayed for mineral content.

It all depends on your application.

For an application that involves creation of colloidal gold deionized water, at minimum, is a requirement.

EDIT:  TYPOS...

[Borek]

i think in the biological aspects of chemistry deionized water is far more stronger in dissolving capacity than distilled water,whose components are soft ions of sulfate after the heavy ions of calcium and magnesium have been scaled by boiling

Please elaborate, you can't remove only cations from solution.

Hand15: depending on the purification method water has almost always some contamination left and is not 100% chemically pure. Characteristics of contaminants depends on the purification method, apparatus used, water used and so on. Also each application has its own characteristics, and water that is OK for one experiment can be bad for other. We are talking about contaminants in the below ppm range.

[shelanachium]

DISTILLATION will remove all non-volatile contaminants from water, e.g. most ionic compounds. But if water is distilled in glass apparatus, the distillate may then dissolve traces of ionic compounds from the glass itself. My old books say that tin apparatus was used to avoid this problem.

Water is DEIONISED by passing it through ion-exchange resins which remove the ions; these will not remove non-ionic contaminants such as most organic compounds.

[Borek]

About twenty years ago we used quartz distillation apparatus to make triple distilled water used for electrochemical experiments. There are no cations that can be leached from quartz.