Distilled water alert

[Photo Engineer]

This thread could go just about anywhere chemistry is discussed because it is important to all of us.

We buy distilled water from many different sources. Recently, I've had a chance to test DW from 4 sources spanning the US from the west coast to the east coast. I have found that the native pH of this water is ranging from 5.0 - 5.9.

Interestingly, DW units are cleaned with either a sulfamic acid derivative or a phosphoric acid solution to remove scale that develops during use. The unit is then flushed completely before being put into use. I have watched this wash and flush take place, and believe me it is a good process which should leave no acidic residue. However, the water that comes out is still at a low pH.

Dissolved CO2 would not lower the pH of DW very much, probably to about 6.5 or so.

Therefore, I have to conclude that the DW retains, on average, some acidic salts or organics for some reason.

I have found no problem with it so far in processing solutions or in emulsion making, but it might affect those who use it for a final rinse instead of photo flo.

And, BTW, tap water from several sources is about 6.5 - 7.5 which is what I would expect from DW under the same conditions.

The bottom line is that DW is not DW, but then again it is apparently OK for use. How odd.

PE

 

[Paul Verizzo]

This thread could go just about anywhere chemistry is discussed because it is important to all of us.

We buy distilled water from many different sources. Recently, I've had a chance to test DW from 4 sources spanning the US from the west coast to the east coast. I have found that the native pH of this water is ranging from 5.0 - 5.9.

Interestingly, DW units are cleaned with either a sulfamic acid derivative or a phosphoric acid solution to remove scale that develops during use. The unit is then flushed completely before being put into use. I have watched this wash and flush take place, and believe me it is a good process which should leave no acidic residue. However, the water that comes out is still at a low pH.

Dissolved CO2 would not lower the pH of DW very much, probably to about 6.5 or so.

Therefore, I have to conclude that the DW retains, on average, some acidic salts or organics for some reason.

I have found no problem with it so far in processing solutions or in emulsion making, but it might affect those who use it for a final rinse instead of photo flo.

And, BTW, tap water from several sources is about 6.5 - 7.5 which is what I would expect from DW under the same conditions.

The bottom line is that DW is not DW, but then again it is apparently OK for use. How odd.

PE

Certainly interesting, but I doubt if modern day DW is actually distilled. When we were kids, DW was hideously expensive because of the energy involved (and transporting glass jugs!) Now, DW is priced right with "drinking water." Why? I presume both are the result of reverse osmosis. Well, I know the drinking and "spring" waters are, generally.

But how would that wind up with acidic pH? Dunno. I'll have to pick up a jug of DW at the store today or tomorrow and check.

 

[Photo Engineer]

Distilled water is distilled. I have watched the process.

PE

 

[clay]

The distilled water I have been buying here in Texas (Ozarka) has a measured pH of 7 everytime I check it on the pH meter. Weird.

 

[craigclu]

I notice terms such as "Processed by steam distillation, microfiltration and ozonation" and some that say by reverse osmosis on various brands. I don't see any that are by straight steam distilling as I had assumed distilled water to be if so labelled. When did the term "distilled" become so flexible as to its definition?

 

[Alex Hawley]

Reverse osmosis is the favored process these days. However, not every water plant has converted to RO, and acid cleaning is still used to remove scale and deposits. Pretty shoddy if the water plant is not adequately flushing after cleaning. Not unexpected though when the management is trying to maximize production, and/or the operators are ill-trained.

 

[Ian Grant]

Yes but some "Distilled water" has never seen a still, often de-ionised water is sold as Distilled water, and it isn't checked or tested properly either.

Good high grade Distilled water for lab use is usually double distilled or de-ionised and then distilled. But many small companies just de-ionise water & sell it as "Distilled" for use in irons & batteries for domestic/garage use, and to be fair it's probably fit for that purpose only.

Ian

 

[jim appleyard]

This thread is quite interesting. I did not know that "distilled" was/is such an umbrella term.

In NY state, Eckerd now Rite Aid was selling water that said "steam distilled". I can only assume this was/is the real deal.

I'll have to check soon to see if they still carry it as I only use it for mixing pyro stocks and those last quite awhile.

 

[Mark Layne]

How about using the water from your basement dehumidifier?
Mark

 

[Ian Grant]

or your air conditioning

Ian

 

[Photo Engineer]

Mark;

Do not use that water. There is a whole thread on the subject from a while back.

As for the rest. I have seen genuine distilled water equipment and the cleaning process by a trained operator. Everything went fine. Still, the production was low pH. The products I tested ranged from Oregon to NY state. The results were the same.

Most products do not have the method of production on the label.

PE

 

[Mike Wilde]

feeling better with my current practice

I gave up on lugging DW jugs home; I'm down on the waste plastic so much bottled water generates that I don;t want to get into it even to buy 'distilled'.

I rehabbed a found on the curb good R/O filter for about $140 a few years ago; now I just change the pre filter every spring, and the carbon polisher post filter every other year. The overflow from the filter is used to pre fill the washing machine when I am around to keep an eye on it.

We use the resulting R/O to mix up powdered milk, and it tastes pretty good that way once it has sat in the fridge overnight. It also has made the kettle heat faster, as very little to no scale builds.

For the darkroom I fill 1gallon glass jugs with it, then pour into a big stainless steel pot and boil it vigorously on the stove with the lid left in place. It cools overnight, and a surprising amount of volume is lost when I put it back to the jug, indicating in part the volume of dissolved gas that was displaced by boiling.

Developers are mixed from the R/O and boiled stock by heating the required amount in the microwave. Then I use cold stock to bring the developerto 1l etc final volume.

I thought I was cutting corners by not buying the DW at the pharmacy/ grocery store and lugging it home.

 

[honeydo]

How about using the water from your basement dehumidifier?
Mark

Huh. I have TONS of that! I water my flowers with it! Silly me....PHOTO! Nah. I'll stick with the filtered water at the lab

 

[RobC]

Mark;

Do not use that water. There is a whole thread on the subject from a while back.

As for the rest. I have seen genuine distilled water equipment and the cleaning process by a trained operator. Everything went fine. Still, the production was low pH. The products I tested ranged from Oregon to NY state. The results were the same.

Most products do not have the method of production on the label.

PE

What makes you think distilled water should have some specific PH?

 

[eclarke]

What makes you think distilled water should have some specific PH?

Because pure water is neutral and is the basis for ph..ph7 by definition...EC

 

[RobC]

Because pure water is neutral and is the basis for ph..ph7 by definition...EC

And what makes you think that distilling makes water pure. I ask because it seems that a lot of people think that is does. It does NOT. Distilling is a process for separating fluids with different boiling points. Anything that boils [edit]below[/edit] the temp you are using will get distilled off. That could be several fluids including chlorine which will get distilled with water.
And distlling does not deionise water and water that has not been deionised will never be PH7. So to put it in a nutshell, I don't understand why the question has been raised in surprise that distilling does not make water a more neutral PH than it does.

 

[Photo Engineer]

What makes you think distilled water should have some specific PH?

From basic chemistry, as stated, the defined pH of pure water is pH 7.0 and thus pure acid is pH 0 and pure base is pH 14. Each step is one order of magnitude and so a pH value of 5 is 100x more acidic than it should be.

Normally, atmospheric carbon dioxide will drop this to about 6.5.

RO water is not distilled water.

PE

 

[RobC]

From basic chemistry, as stated, the defined pH of pure water is pH 7.0 and thus pure acid is pH 0 and pure base is pH 14. Each step is one order of magnitude and so a pH value of 5 is 100x more acidic than it should be.

Normally, atmospheric carbon dioxide will drop this to about 6.5.

RO water is not distilled water.

PE

That still does not answer my question. What makes you think distilled water is 100% pure water?

 

[Trevor Crone]

It was quite common for our laboratory distilled water (using glass stills) to read pH 6.5. It would often read pH 5.5/6.0 on storage because of dissolved CO2.

 

[Alex Hawley]

What makes you think distilled water should have some specific PH?

Its basic chemistry Rob. The ph scale is based on pure H2O, i.e., "distilled", where the H2 and O2 ions are in equilibrium. When the ph scale was devised, that equilibrium was given a value of 7.0, which is the nominal, neutral value. A ph below 7.0 is considered acidic because it has an excess of hydronium ions. Conversely, a ph greater than 7 is considered alkali and has an excess of hydroxyl ions.

Someone check me to see if I explained that right. I'm not a chemist.

In most water treatment processes, the effluent product is passed through ion exchangers to rebalance the ion concentrations following the purification process. Steam distilling produces a pure distilled effluent but it still picks up extraneous ions during condensation on a large scale operation. Producing steam via some sort of power boiler is the most efficient way but has become politically incorrect. And electric powered distilling unit works too but their capacity is not as great as direct steam heating and is thus more inefficient, but on surface appearances, may appear more "green".

Reverse osmosis is quick and has great capacity capability. All of the various processes need periodic cleaning and flushing to remove residues. Virtually all potable water or "drinking water" grade effluents still are not nearly as "pure" as laboratory grade distilled water. That level of purity requires the highest level of production controls, which means highest cost.

Just to put things in perspective, a 1200 MWe steam turbine generator power plant needs about 30,000 gallons per day of make-up water to support the steam plant.

 

[justpete]

FWIW, Wal-Mart Distilled Water label states the following:

Source: Municipal Supply, Ft. Worth, TX
Processed by: Carbon Filtration, Reverse Osmosis, Distillation, UV Treatment, Microfiltration, Ozonation

Checking with pHydrion sticks pH comes out at 5.5 every time and stays at that color with time. Water from the tap comes in at 6.0 every time but color eventually reaches 6.5 to 7.0 within a few minutes.

Water hardness sticks read 0ppm for the distilled water and between 120ppm and 180ppm for the tap water although I've seen it as high as 250ppm in the winter.

Must be the chlorine in the tap water for the acidic pH I guess. I boil the distilled water using teflon boiling stones over a stirrer/hotplate in pyrex flasks and filter w/Whatman #1 circles when making developers but it never occurred to me to check pH. Gotta do that next time.

Tnx, Pete

 

[Ian Grant]

FWIW, Wal-Mart Distilled Water label states the following:

Source: Municipal Supply, Ft. Worth, TX
Processed by: Carbon Filtration, Reverse Osmosis, Distillation, UV Treatment, Microfiltration, Ozonation

Checking with pHydrion sticks pH comes out at 5.5 every time and stays at that color with time. Water from the tap comes in at 6.0 every time but color eventually reaches 6.5 to 7.0 within a few minutes.

Water hardness sticks read 0ppm for the distilled water and between 120ppm and 180ppm for the tap water although I've seen it as high as 250ppm in the winter.

Must be the chlorine in the tap water for the acidic pH I guess. I boil the distilled water using teflon boiling stones over a stirrer/hotplate in pyrex flasks and filter w/Whatman #1 circles when making developers but it never occurred to me to check pH. Gotta do that next time.

Tnx, Pete

Does that mean it's produced by one of those methods rather tan by all

Ian

 

[Jordan]

The RO water at my workplace routinely tests below pH 6.0. Any quantity of water in contact with the atmosphere will absorb CO2, become acidified, and test below 7 with a pH meter. The pH of distilled / deionized water will also depend on temperature (because the solubility of gases in water is temperature-dependent) and probably the path of the water through the purification system (which may promote or discourage air ingestion).

The "definition" of the pH of pure water as pH 7 simply a reflection of the dissociation constant of water but only holds for water with absolutely nothing dissolved in it (no CO2, no salts, etc.) and at 25C... The reaction H2O <-> H+ + OH- has an effective equilibrium constant Kw = [H+][OH-] = 1.0 x 10E-14 at 25C. When you set [H+] = [OH-] (i.e. a neutral solution), both must be equal to 10E-7. pH is then -log[H+] = -log(10E-7) = 7.

Kw depends on temperature; a quick web-search tells me that Kw is 2.4 x 10E-14 at 37C (body temperature) -- going through the calculation suggests that pure water will have pH 6.8 at this temperature, even without any dissolved gases. This is "by definition".

From basic chemistry, as stated, the defined pH of pure water is pH 7.0 and thus pure acid is pH 0 and pure base is pH 14. Each step is one order of magnitude and so a pH value of 5 is 100x more acidic than it should be.

A solution with pH 0 has the concentration of hydrogen ions [H+] equal to 1 mol/L ( -log(1) = 0 ). Assuming an ideal solution, 1 M HCl will have pH 0. A 2 M HCl solution will have pH -0.3. Although these are concentrated solutions that can do a lot of damage, both of them are far from being "pure acid". Things get hairy in really concentrated solutions where concentration does not directly translate into pH, but it is certainly very possible to go below pH 0 and above pH 14 in water.

To identify the cause of acidification in purified water, I'd want to try to following before claiming that there is contamination:

• Either boil the water or sparge it with nitrogen to drive off CO2, and see if the pH or especially conductivity changes (after cooling in a filled container, of course). The conductivity of water is what is routinely used to assess deionization.
  
• If phosphoric acid is a suspected contaminant, try precipitating it with something like barium chloride. Barium salts should precipitate phosphates and become cloudy (just like silver nitrate precipitates the traces of chloride in tap water). I'd imagine sulfamic acid would behave similarly.

Hope this helps

 

[Paul Verizzo]

Recently?

Distilled water is distilled. I have watched the process.

PE

Recently? At one of the major water distributors?

Why would it be so cheap?

 

[Kvistgaard]

Mark;

Do not use that water. There is a whole thread on the subject from a while back.

hi Photo Engineer - would you happen to have a URL to that thread? I'd like to read it, because I have been using the water from our tumble dryer, which works by condensing the water from the wet clothes. I'd assume that whatever problems water from a basement de-humidifier has, water from my tumble dryer has as well.

I've been using the water from the dryer to wash my negatives after development, not for mixing chemicals.

Thanks.