is rainwater comparable to demineralised water?

hoffy · Feb 16, 2013

As the title suggests, is captured rain water comparable to demin water?

My father used to catch rain water on the back lawn in plastic containers and always told me that it was just as good.

Was he right?

markbarendt · Feb 16, 2013

Precipitation naturally condenses around impurities in the air, dust, ash, and other stuff. Downstream of power plants in the eastern USA we famously had/have acid rain. So the answer is that it depends on what it's condensing around and pulling out of the air.

quejai · Feb 16, 2013

Demineralised water is more pure than rainwater is more pure than tapwater.

If you live in an urban environment, it's closer to tapwater from absorbing carbon dioxide (turns it to weak carbonic acid) and etc from pollution in the air.
If you live in a rural place, it's much closer to demineralised water.

Either way, wait out the first 10 minutes or so of rain to 'wash out' the air, and then collect water after that. It's the cleanest you're going to get.

hoffy · Feb 16, 2013

quejai said:
Demineralised water is more pure than rainwater is more pure than tapwater.

If you live in an urban environment, it's closer to tapwater from absorbing carbon dioxide (turns it to weak carbonic acid) and etc from pollution in the air.
If you live in a rural place, it's much closer to demineralised water.

Either way, wait out the first 10 minutes or so of rain to 'wash out' the air, and then collect water after that. It's the cleanest you're going to get.

OK, so my father was kind of right, because we lived on a farm in a rural area, 150KM away from the closest city.

But for me....OK, I suppose I would also then need to consider filtration, which in the end might just end up being just as easy to buy the 4 litre bottles from the super market.

Gerald C Koch · Feb 16, 2013

Even if you live in an area with very hard water you can soften it by vigorously boiling tapwater for 5 minutes and allowing it to stand overnight. The temporary hardness (calcium ions) will precipitate out. The permanent hardness (magnessium ios) have no effect on photographic uses. The next day decant or filter off of the clear portion for use in developers.

hdeyong · Feb 17, 2013

I collect and use rain water, (we live a good distance from any cities), and have had good results. We have a lot of limestone in the water here, so I use the rain for a final rinse and with the wetting solution. I'm pretty sure the film is drying a lot cleaner. But, as a couple of people have noted, I wouldn't even think of it in a big city.

adelorenzo · Feb 17, 2013

I only drink distilled water, or rainwater, and only pure grain alcohol.

hoffy · Feb 17, 2013

adelorenzo said:
I only drink ...... pure grain alcohol.

Fixed it for you! (OK, maybe I am thinking about me and maybe this is wishful thinking!)

Marc B. · Feb 17, 2013

Another source for what is basically distilled water is the ice build-up you have to chip away from a freezer.
(De-frosting a non, frost-free freezer, of course). If you're in the city, I'd just buy the distilled bottled water.
I suppose the photography folks living in Bermuda have it easy, (for distilled/demineralized water),
as the Island's entire water supply is captured rain water.

Marc

bobwysiwyg · Feb 17, 2013

Acid rain falls everywhere. Rain water is hardly what I would consider pure chemically.

Gerald C Koch · Feb 17, 2013

Not all air pollution is particulates. There are also dissolved gases; sulfur dioxide, various oxides of nitrogen, hydrocarbons, etc.

fotch · Feb 17, 2013

Gerald C Koch said:
Even if you live in an area with very hard water you can soften it by vigorously boiling tapwater for 5 minutes and allowing it to stand overnight. The temporary hardness (calcium ions) will precipitate out. The permanent hardness (magnessium ios) have no effect on photographic uses. The next day decant or filter off of the clear portion for use in developers.

I would think the cost of heating, boiling water would exceed the cost of just buying distilled water, unless it just not available where you live.

drumlin · Feb 17, 2013

adelorenzo said:
I only drink distilled water, or rainwater, and only pure grain alcohol.

"I do not avoid women, Mandrake...but I do deny them my essence."

Greatest movie ever.

Rafal Lukawiecki · Feb 17, 2013

drumlin said:
"I do not avoid women, Mandrake...but I do deny them my essence."

POE

Vaughn · Feb 17, 2013

I used rain water to develop negs in Austrailia. The house on the farm was no longer being used (but made a decent darkroom until the lightning storm came by). I had to use milk filters to filter out the various larve, but the negs came out fine. I had to stop while the storm was nearby, as the window coverings were not 100% light tight.

Oxleyroad · Feb 17, 2013

Ash,

My darkroom only uses tank water. Came about as a result of our water restrictions we had several years back.

The tank water goes through four filters. A 20µm washable screen filter takes out all the big bits from the tank water and this water is also used for the toilet and washing machine. Then in the darkroom there is an under sink unit with a 1µm wound fibre to get rid of the sediment, a mixed bed resin filter for heavy metals (there is a lot of lead on my roof) and finally 0.5µm carbon block filter. I change the filters in the darkroom every 12 months.

It works for me. But I have never measured the pH nor have I bothered to see what might still be there.

Gerald C Koch · Feb 18, 2013

fotch said:
I would think the cost of heating, boiling water would exceed the cost of just buying distilled water, unless it just not available where you live.

It would all depend on how much each person pays for electricity or gas. Distilled/de-ionized water runs $1.00 to $2.00 per gal here in the US. Ads for electric home distilling machines claim to produce a gallon for $0.25. So boiling a gallon of water for 5 min should certainly cost far less than this. From a similar thread not so long ago some people in Europe pay exorbitant prices for distilled water if it is availale at all. .

hoffy · Feb 18, 2013

Oxleyroad said:
Ash,

My darkroom only uses tank water. Came about as a result of our water restrictions we had several years back.

The tank water goes through four filters. A 20µm washable screen filter takes out all the big bits from the tank water and this water is also used for the toilet and washing machine. Then in the darkroom there is an under sink unit with a 1µm wound fibre to get rid of the sediment, a mixed bed resin filter for heavy metals (there is a lot of lead on my roof) and finally 0.5µm carbon block filter. I change the filters in the darkroom every 12 months.

It works for me. But I have never measured the pH nor have I bothered to see what might still be there.

Thanks Andy,

For general all purpose chemical dilution and mixing, I use filtered tap water, except for doing colour. I have always used Demin water for the final rinse when developing film. I have found that this is the best way to ensure clean streak free negs. I had thought of using demin for the whole process, but the price of buying 4 litres at a time has put me off.

I believe Polyglot uses bottled spring water (for the chems at least), but I believe his tap water is really quite bad.

RattyMouse · Feb 18, 2013

Gerald C Koch said:
Even if you live in an area with very hard water you can soften it by vigorously boiling tapwater for 5 minutes and allowing it to stand overnight. The temporary hardness (calcium ions) will precipitate out. The permanent hardness (magnessium ios) have no effect on photographic uses. The next day decant or filter off of the clear portion for use in developers.

Incorrect. Boiling the water increases the hardness up until you reach the saturation point, and then salts will begin to precipitate out. You will be left with severely hard water.

Magnesium and calcium ions act have almost the same reactivity.

Gerald C Koch · Feb 18, 2013

RattyMouse said:
Incorrect. Boiling the water increases the hardness up until you reach the saturation point, and then salts will begin to precipitate out. You will be left with severely hard water.

Magnesium and calcium ions act have almost the same reactivity.

??? NO on all counts.

The temporary hardness in ground water comes from the presence of soluble calcium bicarbonate. When the water is boiled briefly this compound decomposes to form calcium carbonate which is insoluble. All cacium salts are effectively removed from the water. Calcium in water used in photographic solutions can causes problems with high sulfite containing developers like D-76 where it precipitates out as calcium sulfite and in carbinate containing developers like D-72.

Magnesium compounds are soluble and only affect water when soaps are used for washing. Both calcium and magnesium form insoluble soaps which stick to cloth fibers. Magesium salts in water are not a concern in photography.

Noble · Feb 18, 2013

adelorenzo said:
I only drink distilled water, or rainwater, and only pure grain alcohol.

While minerals in water may have an adverse effect on the film development process your body needs them. A little calcium is good for your bones. Try spring water.

Gerald C Koch said:
From a similar thread not so long ago some people in Europe pay exorbitant prices for distilled water if it is availale at all. .

Why is this? In some European countries it's a pain in the @$$ to get distilled water and in the US it is sold all over the place by the gallon (milk and petrol are sold by the gallon as well). I use distilled water at various points in the processing workflow. What is everyone else using it for?!

Oxleyroad · Feb 26, 2013

Ash,

I understand you are/might be coming to Melbourne early March. You have to look me up if you have the time and I can show you the set up and the darkroom.

RattyMouse · Feb 27, 2013

Gerald C Koch said:
??? NO on all counts.

The temporary hardness in ground water comes from the presence of soluble calcium bicarbonate. When the water is boiled briefly this compound decomposes to form calcium carbonate which is insoluble. All cacium salts are effectively removed from the water. Calcium in water used in photographic solutions can causes problems with high sulfite containing developers like D-76 where it precipitates out as calcium sulfite and in carbinate containing developers like D-72.

Magnesium compounds are soluble and only affect water when soaps are used for washing. Both calcium and magnesium form insoluble soaps which stick to cloth fibers. Magesium salts in water are not a concern in photography.

Thank you for informing me of this.

hoffy · Feb 27, 2013

Oxleyroad said:
Ash,

I understand you are/might be coming to Melbourne early March. You have to look me up if you have the time and I can show you the set up and the darkroom.

Its the easter weekend - Not sure if I have time, as I am travelling with someone else, but if I do, I'll be in contact!

Oxleyroad · Feb 27, 2013

hoffy said:
Its the easter weekend - Not sure if I have time, as I am travelling with someone else, but if I do, I'll be in contact!

Bother, the Easter w/e is when the family and I are out of town - up in Mildura. Next time hey.

is rainwater comparable to demineralised water?

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