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Distilled v. De-Ionised water for mixing developers

stephen jones , Sep 12, 2002; 03:21 p.m.

In a previous thread, on Fx50, I mentioned that I used bottled water to mix my solutions. In one of the responses it was asked why I didn't use distilled water. The answer to this is that it is simply not available (as far as I can tell) in the UK. De-ionized water is invariably offered as an alternative. However, on page 190 of The Negative (A.Adams esq.) he counsels against the use of "softened" water saying that the removal of Calcium (as well as its exchange for other ions) is not ideal for photographic developers: "after softening, [the water] may have only 20ppm [of Ca++]. I understand that 180 to 200 ppm of calcium is ideal for most photographic processes." So, my questions are a. am I correct in thinking that de-ionized water has its calcium exchanged for sodium? b. is AA correct that it's needed? c. where can I get truly "distilled" water in the UK?


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Gannet -- , Sep 12, 2002; 04:21 p.m.

I can't speak to the UK situation (so maybe I should shut up, right? grin), but I do know something about water purification.

The softened water Adams refers to is what you get after you run water through a water softener: big cylindrical thing, looks like a water heater, with special salts inside. In the US at least, this is normally only used in homes that have hard well water (there are exceptions).

Do you buy your "de-ionised" water at the local market? That's the way it's usually done in the US. Here, the stuff is sold as "purified water". This water is produced by reverse osmosis filtering, usually coupled with additional charcoal and possible resin filtering. It is actually better than consumer-grade distilled water for virtually all purposes, and the economics of its production have driven true distilled water from the market most places. If this is what you get, it'll be just fine for photo purposes.

Marine aquarists have to deal with this issue (which is why I know about it). Ask at the local specialist aquarium shop (not a "pet store") and they should be able to direct you to a supply.

Mark Farnsworth , Sep 12, 2002; 04:30 p.m.

Right before the part you quoted, Adams says: "Water of a pH of 7(neutral) is ideal. Distilled water is not exactly pH7, but is free of metallic ions and organic substances, and is adequate for mixing all developer solutions."

In parts of the USA, the water is extremely hard (rich in minerals) and is softened by municipal water systems, or in some cases by water softeners in individual homes. I believe that this is what Adams was referring to when he warned about water softeners. I don’t really know how water labeled as “distilled” in the USA compares to ionized water in the UK. A bottle I purchased says that it was processed by distillation, micro-filtration and ozonation. I think most people recognize that such water is not 100% pure as would be used in a scientific experiment that called for pure H2O. In the USA, “distilled” water is available at most grocery or discount stores in plastic one-gallon jugs for $0.75 USD or less.

stephen jones , Sep 12, 2002; 04:50 p.m.

Mark, but Calcium is not a metallic ion. If calcium is needed for the process, is removed by de-ionization but not by distillation, then I shall be in trouble. (unless somebody can recommend me a supplier of distilled in the UK)

john baxendell , Sep 12, 2002; 05:12 p.m.

Any chemist (drugstore) in the UK will sell you distilled water. They give you funny looks but they charge so much that they don't ask too many questions. If it is not on display ask the pharmacist. When I was in the States I was amazed to see how cheap distilled water is in places like Duane Read. I am also interested to know if people advocate using distilled water to mix developer.

Philip Glass , Sep 12, 2002; 05:28 p.m.

Wal-mart sells distilled water for 58 cents per gallon in the U.S. Not exactly prohibitive. We will not be happy until all of the U.K. is Wal-Marted and Wal-watered.

Jorge Gasteazoro , Sep 12, 2002; 05:36 p.m.

Ok, first let me clarify somethings about deionized water as there seem to be lots of inaccurate information in these answers.

To obtain deionized water, the water is passed through two different beds composed of resins, not specialized salts! The cationic resin bed is also what is commonly used in water sofeteners in their sodium salt state. Normally for deionized water the cationic bed is in its Hydrogen state, meaning that as the cations are exchanged hydrogen is released, not sodium as it happens with a water sofetener. The water is then passed through an anion bed which removes the anions from the water and releases hydroxy groups, thus when the process is complete you get water. Of course this process is not 100% effective and there is some leakeage, usually this leakeage is small enough as to no make any difference in the prorcess. Let me put it this way if it is good enough for a nuclear plant, it should be good enough for your photo needs.

OTOH the purest kind of water is distilled water, but the difference between distilled and de ionized water is so small that the additional expense to distill the water is not worth the benefits. At least in industrial and analytical settings. For photography you should not worry about getting distilled water, deionized is plenty pure for your requirements.

Adams was correct in the sodium form cationic resin will trap calcium ions and release sodium ions, since sodium forms a "soft" scale with carbonate then you dont get that ugly hard scale on your sinkm bath etc. What is the effect effect of removing the calcium ion? well very simplu put you affect the ph of the water, making it more acidic and lowering the efectivness of the developer. Finally to your last question you are incorrect, de ionized water has the calcium ion exchanged for hydrogen ion, and subsequently the anionic species are exchanged for hydroxy ions, thus removing all salts from the water. This is why the process is so useful!

Edward Zimmermann , Sep 12, 2002; 06:14 p.m.

  • Most of the developers have substances like calgon (Sodium Hexametaphosphate) to sequester calcium.
  • to quote my 1939 Agfa Handbook "Distilled Water is Pure Luxury"... where it goes on to describe how to filter and decant water.
  • Distilled and de-ionized water are "different beasts". For photochemical applications you want, if at all, distilled water. Distilled water is available in different qualities (also sterile) from "Apoteke(n), Chemists, Farmacia, Pharmacies, etc."....

Jorge Gasteazoro , Sep 12, 2002; 07:59 p.m.

Distilled and de-ionized water are "different beasts". For photochemical applications you want, if at all, distilled water

There have been many advances since 1939.....one of them is in the use of zeolites and susequently the manufacturing of cross linked resins for ion exchange. The difference between destilled and de ionized water is merely in the degree of lekeage from the deionization beds. You do not need destilled water, deionized water is good enough, the difference in degree of purity between destilled water and deionized water is less than .01 micro mhos of conductivity, translated to total disolved solids, we are talking about 2 to 3 micrograms, harldy an amount to make a difference!

Sterile distilled water only means that appropiate measures were taking to remove bacteria, which are not removed by the deionization process, and has nothing to do with degree of salts removal.

Bob Finley , Sep 12, 2002; 10:57 p.m.

Jorge is right on target. For developing I have been using deionized water for some time instead of distilled as I can get it for 25 cents per gallon at my saltwater fish store. I check it with a refractometer occasionally and it always shows a "0" specific gravity.

It is my understanding that here in the U.S. when you buy grocery store containers of distilled water for steam irons etc. you are actually getting deionized water.

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