Old Distilled Water in Half Empty Bottle...Acidic?

[John Layton]

I currently have two gallon plastic jugs of distilled water, which have been sitting on my darkroom shelf for about six months. One of these bottles is full, the other about half full.

Question: during the course of six months…would the half full bottle of distilled water have absorbed enough C02 from the air in its bottle to become acidic?

I’ve been wondering about this for a long time…and I ask this because I’ve just decided to give Formulary TF-5 a try as a potential replacement for TF-4 - and my understanding is that TF-5, while slightly alkaline, is a bit less alkaline than TF-4, and thus were I to mix TF-5 concentrate with acidic water I might end up with less build up of the wonderful image stains possible from PMK and Pyrocat developers.

Am I overthinking this?

[Michael R]

It doesn't matter.

Water has virtually no buffering capacity. For example water might come out of a tap at pH 8 (weakly alkaline) and then fairly quickly go down to pH 6 (weakly acidic) in open air. And none of this matters at all. Whatever pH the water is at will be totally overwhelmed by the acid/base/buffering compounds in your fixer concentrate etc. It is also worth noting the target pH of any particular photo solution can drift at least slightly and has some leeway - particularly in the case of sundries such as fixers.

TF-5 is not alkaline but neutral (in fact target pH is slightly acidic ie pH 6.5-6.8), whereas TF-4 is alkaline, and this doesn't matter either when it comes to imagewise stain from PMK or Pyrocat. There will be no difference.

[John Layton]

...and likewise there would be no difference (no negative effects on image stain) were I to use this old, half-empty bottle of distilled water (assuming its become acidified) to dilute my PMK or Pyrocat liquid concentrates?

[Michael R]

...and likewise there would be no difference (no negative effects on image stain) were I to use this old, half-empty bottle of distilled water (assuming its become acidified) to dilute my PMK or Pyrocat liquid concentrates?

As far as alkalinity/acidity goes, no problem. Water pH is is a non-issue.

[Drew Wiley]

The stain that counts occurs in the development step, wherein the pH effect of its own ingredients is going to be so dominant that most tap water issues won't have any significant effect, unless perhaps, you're well happens to be in Death Valley beside an old borax mining pit.

There are certain now rare color processes where minor pH water differences can have a substantial impact; but in this case, yes, you are overthinking it. I ditto Michael, not as a hypothetical absolute answer applying to all photographic processes, but as a valid practical answer to your specific question. In fact, here I only use distilled water for the final film rinse before hanging the film to dry.

[Michael Wellman]

CO2 content in air is only 0.04%, so in an open container you would get a very low amount of CO2 absorbed. The fact that it is in capped plastic bottle means that there is no CO2 being transferred. As others have pointed out this is not a problem for TF4/TF5