How critical is developer water pH?

I live just north of Austin, Texas in Round Rock. About two thirds of our water comes from streams which flow through limestone. The balance is pumped groundwater. Probably the same calcium load.

In the years that I've owned a pH meter I've observed that tap and bottled water can have wide ranging pH's. Here are a few examples:

Municipal water where I used to live, Sarasota FL. Best as I can recall, about 6.8. Roun' there. Under 7.
Municipal water, Round Rock, TX: 7.2 Sort of amazing, it has a LOT of lime in it as evidenced by crud on dishwasher dishes. To counteract this, I put a tablespoon or more of citric acid in the final rinse. Wow! Big difference.

RO water from a bulk dispenser, 7.2

"Distilled" grocery store water, 7.6 . I put distilled in quotation marks because I doubt if it is steam distilled at under $2/gallon. Probably just tighter spec'd RO.

"Drinking water," 7.6

That's a HUGE range in terms of activity! And I'm sure there are many locations that have both higher and lower pH's.
Possibly how different photographers in different location find such variations in, at the least, developing times.

Water pH is not critical, it is very poorly buffered.

Paul Verizzo said:

Distilled" grocery store water, 7.6 . I put distilled in quotation marks because I doubt if it is steam distilled at under $2/gallon.

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You are right. It’s not destilled, it’s only demineralized. Most probably by reverse osmosis membrane

From my laboratory days in electro-chemistry: Fundamentally it is not possible to do a straight forward measurement of the pH of pure water using a standard combined glass bulb pH probe.
The ionic strength of pure water is so low that the pH probe does not reach a stable electrical potential that the pH meter can measure and display as a pH reading.

As Anon Ymous points out pure water, theoretically pH 7, has negligible buffering capacity (i.e. the capacity to resist pH change) so the tiniest contamination can cause large pH changes. The usual contaminant for water in contact with air is dissolved carbon dioxide which can cause the pH to go below 7 in seconds.
For pure water stored in glass the contamination is usually sodium and calcium ions leached out of the glass and then the pH rises above 7.

For those who really want to measure the pH of pure water the answer is to add a few drops of concentrated potassium chloride solution. This boosts ionic strength and ion mobility without changing the pH. Now the pH probe can settle to a stable and reproducible potential that the meter can display as pH. But the water sample isn't pure anymore, darn.

From a photographic point of view the buffering capacity of pure water, tap water, even well water is so low that its starting pH is totally (totally!) overwhelmed by chemical components dissolved in it that make for a photographically active developer.

Maris said:

From a photographic point of view the buffering capacity of pure water, tap water, even well water is so low that its starting pH is totally (totally!) overwhelmed by chemical components dissolved in it that make for a photographically active developer.

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Thank you Maris for the explanation. This makes sense.

Most developers have fairly strong alkali in them (the developing reaction occurs in an alkaline environment), which overpowers the modest acid or alkali pH of plain water, as Maris and others said.

Where one might be a little more concerned is with the salts in the water, not simply its native pH. For ex, hard water typically has a lot of calcium carbonate, like yours, and carbonates are used as the alkali in many developers, so in principle having extra carbonate might affect the equilibrium concentration. In practice, it's generally believed that commercial developers are formulated to be well buffered and/or sequester extra salts to achieve their design concentration/pH in a wide range of tap water. However, if one is mixing developers from scratch, it might be wise to use distilled/demineralized water.

Here's an informative post from Doremus Scudder on hard water: https://www.photrio.com/forum/threads/lime-in-the-water-is-this-a-problem.190432/post-2527505

I live in a place with hard water and questionable pipes, and I usually use generic distilled water to mix developer stock solution (Here I'm concerned about iron from the pipes killing Xtol or similar developers), and for the final Photo-flo rinse. I use tap water for all the other solutions. Also, if I have to drop a couple of tap water ice cubes into the working developer to bring it down to temp, which happens a lot, I do that and don't worry about it.

reddesert said:

I live in a place with hard water and questionable pipes, and I usually use generic distilled water to mix developer stock solution (Here I'm concerned about iron from the pipes killing Xtol or similar developers), and for the final Photo-flo rinse. I use tap water for all the other solutions.

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Exactly the same situation here where I am living and the same procedure

@Paul Verizzo Different photographers use vastly different development times because (IMHO) they have no point of reference to begin with. Their methodology can be totally different and there's not a single definition of what is accepted as "normal". To make things even worse, thermometer variation can also affect development times. Add sloppiness, inadequate equipment etc and you'll realise the futility of it.

That said, do we really need this level of exactness to get perfectly usable BW negatives? Certainly not.

Paul Verizzo said:

That's a HUGE range in terms of activity!

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No. It's a huge absolute difference in the concentration of OH- or H+ ions, but on the larger scheme of things the differences you describe are vanishingly small. See @Maris' explanation for details.

Paul Verizzo said:

Possibly how different photographers in different location find such variations in, at the least, developing times.

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Differences in pH of the water used by no means explain these things. If the parameters @Anon Ymous mentions are controlled tightly, you and I would really observe the exact same densities from the same amount of exposure on the same film developed in the same way with the same developer, even though your water may be hard and mine soft, or vice versa. It won't make one iota of difference.

I'm in San Antonio and we have city well water. As others have noted, pH is really not much of an issue but dissolved limestone (scale, etc) is the real issue. I use either HEB distilled water (locally grocery for those not in Texas) for pre-wet, developer and then tap water run through a whole-house softener and RO for all the rest of the chemistry and steps. The final rinse is usually a minute in distilled and then photo-FLO in distilled as well. Negatives are clean and dry down without spots. If I take water directly from the aquifer, it produces scale even in one glass after it evaporates.

Paul Verizzo said:

Possibly how different photographers in different location find such variations in, at the least, developing times.

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While it may be or may be not interesting for you to see the "science" for water PH I got the impression your thread is seeking experiences from Photrio members in terms of whether it makes a practical difference to the development process

Assuming I have interpreted your prime requirement correct then here's mine. I live in one of the hardest water areas in the U.K. and need to descale my kettle every few weeks but in 17 years of home developing a variety of films I have never experienced a problem or found any need to alter anything about my process by way of any form of compensation

I have never found the need to use distilled/de-ionised water at any stage

It might make sense to re-emphasise that your need to is to get actual experiences from us if this is the main purpose of your thread


pentaxuser

I thank all of you who know chemistry better than me for why my fears.......or theories....are ungrounded.

BCM said:

I'm in San Antonio and we have city well water. As others have noted, pH is really not much of an issue but dissolved limestone (scale, etc) is the real issue. I use either HEB distilled water (locally grocery for those not in Texas) for pre-wet, developer and then tap water run through a whole-house softener and RO for all the rest of the chemistry and steps. The final rinse is usually a minute in distilled and then photo-FLO in distilled as well. Negatives are clean and dry down without spots. If I take water directly from the aquifer, it produces scale even in one glass after it evaporates.

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While I'm no Martha Stewart, I was amazed at how much water spotting happened in my dish washer. I found the stuff you put in the dispenser both expensive and not very good. I used my photo chemistry knowledge, such as it is, and now add 1-2 TBL's of citric acid into the final rinse. Not only are there no water spots, all of the plates and utensils feel smooth!

Paul Verizzo said:

While I'm no Martha Stewart, I was amazed at how much water spotting happened in my dish washer. I found the stuff you put in the dispenser both expensive and not very good. I used my photo chemistry knowledge, such as it is, and now add 1-2 TBL's of citric acid into the final rinse. Not only are there no water spots, all of the plates and utensils feel smooth!

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And any development that might have occurred is stopped right away!

MattKing said:

And any development that might have occurred is stopped right away!

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I wonder if that's why I can't get an image........

I'm gonna attach an excerpt from the only published water quality paper that I know of... it's from 1965, by Lloyd West of Kodak...
Basically the same thing as what other posters have already said..

Paul Verizzo said:

While I'm no Martha Stewart, I was amazed at how much water spotting happened in my dish washer. I found the stuff you put in the dispenser both expensive and not very good. I used my photo chemistry knowledge, such as it is, and now add 1-2 TBL's of citric acid into the final rinse. Not only are there no water spots, all of the plates and utensils feel smooth!

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Water spotting in a dishwasher is calcium deposits and not any indication by itself that the pH is off 7.0.

Sirius Glass said:

Water spotting in a dishwasher is calcium deposits and not any indication by itself that the pH is off 7.0.

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No argument. As I think I mentioned all of the water here flows out of or through limestone.

Paul Verizzo said:

No argument. As I think I mentioned all of the water here flows out of or through limestone.

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The water in the Canadian Rockies flows through limestone as well. I use tap water for everything in my darkroom.... no negative (sic) results....

GregY said:

The water in the Canadian Rockies flows through limestone as well. I use tap water for everything in my darkroom.... no negative (sic) results....

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That has been my experience as well in similar conditions. I lack only the Rockies and Gordon Lightfoot in my part of the world, although within walking distance of my home I can stand on the highest point on the Earth's surface in a due Easterly direction until the Ural mountains in the Russian Federation some 2,300 miles distant

It is a wild place with no habitation for maybe half a mile or so( that constitutes wild in the East of England.). I practice "The Wreck of the Edmund Fitzgerald" until the police take me away frequently

pentaxuser

Posts that say that the buffering capacity of pure H2O is negligible are right on the mark, so even the addition of a tiny amount of pure acid or base will overwhelm the 0.1 micromolar amount of H+ in pure distilled water. The same goes for the addition of even a weak buffer.

Now for a bit of esoteric science related to pH. It was mentioned that adding a bit of potassium chloride chloride to the solution will increase the ionic strength (which is true) without changing the pH (which is not quite true.) Changing the ionic strength will change the pH, even if the hydrogen ion concentration does not change. How much it changes is a function of the ionic strength. If the ionic strength is extremely low then the pH won't change much, only a little. However, the log of the hydrogen ion activity (which is what determines the pH) varies with the square root of ionic strength in the realm of low ionic strength.

Anyway, it turns out that even the fundamental definition of pH is fraught with difficulties because it is based on the logarithm of the hydrogen ion activity. (Here I refer to "activity" as defined in chemical thermodynamics, which takes into account that the free energy of a reaction depends only approximately on the concentrations of the species taking part in a reaction. "Activity" is a kind of fudged version of concentration that is sort of a correction to the concentration to make the thermodynamic equations true.)

The problem with pH is that, as noted above, it depends on the logarithm of the hydrogen ion activity. This means that it depends on the activity of an ion. (I will call this the single ion activity, not in the sense of an ion count of one ion but in the sense of considering only the hydrogen ion and not any counter ion.) But traditionally single ion activity has been considered thermodynamically undefineable and therefore a physically meaningless quantity, even in principle.

Where am I going with this? A few years ago I published a paper showing that single ion activities, if properly defined, are thermodynamically defineable and measurable. This puts the concept of pH on a thermodynamically stable footing for the first time. The title of the paper is "Meaning and Measurability of Single-Ion Activities, the Thermodynamic Foundations of pH, and the Gibbs Free Energy for the Transfer of Ions between Dissimilar Materials" It was published seven years ago in Chemphyschem. If you are a P-Chem junkie, and especially a chemical thermodynamics junky you might get a kick out of reading the paper. It takes a very classical thermodynamic look at the problem and works through the problem in great and rigorous detail. I like to tell myself that Josiah Willard Gibbs himself would be proud of the paper. The paper is freely downloadable.

I like to draw the attention away from the direct effect of water pH on the developer to its effect on tubings.

This may lead to heavy metals as copper and lead being leached into the tap water. At iron already was hinted in this thread.