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Reverse Osmosis (RO) Water vs Distilled Water for Film Processing

vicb

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Location
Paris
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35mm
Hi everyone,

I was wondering if anyone here has experience with reverse osmosis (RO) water filtration systems, particularly the Everpure MRS-600HE-II. Is it worth investing in one when processing high volumes of film daily? How does RO water compare to distilled water?

If so, which parts of the process is RO water typically used for, and how often are the filters replaced in practice? I understand they’re generally changed about every six months, but I’d love to hear how this works in real-world use.

Thank you very much!
 
Virtually all photochemistry is formulated to work with tap water. The water you draw from the tap in Paris is perfect for this.

The only position you might consider demineralized water for is the final rinse. Whether it's worthwhile to install a RO or other purification system for this depends on the local cost of demineralized water delivered in bulk vs. the CapEx and OpEx of the water treatment system of your choice.

Btw, I'll move this to a more appropriate subforum as it's not specific to color processing.
 

The simple water jug deionisers are more than sufficient for darkroom use, I have to use one in the house to stop Calcium build up in the kettle as our water supply is very hard.

Ian
 
I'm on a private well with high iron content and use a salt softening system, I use tap for most processes and distilled for mixng chems to stock solution and final rinse of film, I dilute stock to working with tap water.
 

Okay, thank you!

And I appreciate you moving the post to a more suitable subforum!
 
Ian Grant said:
The simple water jug deionisers are more than sufficient for darkroom use, I have to use one in the house to stop Calcium build up in the kettle as our water supply is very hard.

Ian
Click to expand...
Thanks, that makes sense! It’s good to know that even simple deionizers can handle hard water for darkroom use. I’m mainly curious about what purified water actually does in practice - like how much of a difference it makes for the final rinse, and how often it needs to be replaced in a busy workflow.
 
Rick A said:
I'm on a private well with high iron content and use a salt softening system, I use tap for most processes and distilled for mixng chems to stock solution and final rinse of film, I dilute stock to working with tap water.
Click to expand...

Do you use D&D machine for processing as well?
 
vicb said:
I’m mainly curious about what purified water actually does in practice
Click to expand...
Not a whole lot, really.
The main causes for problems in untreated tap water are:
1 Calcium salts that leave marks on dried film
2 Iron salts that negatively affect developer lifetime
3 Potentially chloride ions that affect developer activity

No 3 is generally not really a concern on most municipal water systems as the chloride content is too low to have a significant impact.
No 2 is generally not really a concern because the photochemistry and replenishment rates are formulated to account for the presence of some iron.
No 1 is in practice the most problematic one, and IMO the only sensible rationale to use demineralized or deionized water in your application, even though there are strategies for managing this issue even if tap water is used; e.g. a proper finishing regime and use of a final rinse formulated to work well for the purpose. In your other thread, you're in the process of addressing this issue, and I think that also emphasizes that deionized water is not a panacea for such problems to begin with.

Of course, if you have a cheap and easily available source (internally or externally) for demineralized/deionized water, nothing bars you from using it also to mix other chemistry and not just for a final rinse. That's up to you to decide.

That's my take on it at least; I'll happily stand corrected on any inaccuracies or omissions on my behalf.
 
I use distilled water to mix all chemistry that will be stored for later use and as a final rinse of my film. RO water is used for all general processing and tap water for washing both film and prints. No specific reasons for RO vs tap water, other than the RO water seems "cleaner" to me.
 
I use reverse osmosis water from my kitchen tap for basically all my photochemistry. Our water has pretty high TDS and when I'm mixing stuff from scratch I can omit the sequestering agents (which i tend to not have anyway)

I also do my final rinse with just reverse osmosis water and that seems to be sufficient to avoid water spotting.
 
It depends on your tap water quality, specially the hardeness. There are zones with very hard water (typical in Spanish Mediterranean coast) and the photo chemistry is your least concern. It is unpleasant to drink and causes problems in taps and shower heads. In those cases RO, deionized and/or bottled water is the only way to live.

Commercial developers try to address unsuitable traces in your water with additives (chelatin agents mostly). Besides that, there are the stains after the final rinse. If you don't see any, you are good to go with whatever water you are using.

I am fortunate enough to have a good quality tap water that I use almost for everything, including color final rinses. I only use (cheap) deionized water for the BW final rinse, the product requires to not squeeze at all after the bath (Rollei RWA SC).

By the way, Kodak published some guidelines of water quality in the famous Z-131 document. The published analysis of my tap water complies with it.

 
Something else worth adding is that wetting agent concentration is specified for use with in-spec tap water (as per the Kodak documentation posted above by @halfaman ), not distilled water - which is something I've run up against in the past.

Outside of emulsion making and certain scratch-mixing (if you don't have certain sequestrants, and if those sequestrants aren't essential to the process - e.g. some B&W reversal or ascorbate developers) of process/ toning chemistry, distilled water should not be needed apart from for things like (possibly) print spotting etc.
 
vicb said:
Do you use D&D machine for processing as well?
Click to expand...

What's D&D machine? I rotary process my LF film in Unicolor drums on a self-reversing motor base, and small single reel SS tanks for roll film.
 
koraks said:
Not a whole lot, really.
The main causes for problems in untreated tap water are:
1 Calcium salts that leave marks on dried film
2 Iron salts that negatively affect developer lifetime
3 Potentially chloride ions that affect developer activity
Click to expand...

I would add dissolved solids/particulates to this list.
 
I have to use RO water for everything here on the farm because the water is unusable as it comes out of the well: so much iron that it gradually ruins everything it touches.
As others have said, when making chemistry for film processing, it depends on your water quality whether buy can use tap water or not.
 
I just want to ask whether it’s very costly to change the filters and how often it needs to be done (approximately), because I’ve heard a couple of different versions.
 
vicb said:
I just want to ask whether it’s very costly to change the filters and how often it needs to be done (approximately), because I’ve heard a couple of different versions.
Click to expand...

I don’t think I can give you a meaningful answer, because you’re asking about a small RO unit, whereas in my case it’s a huge system that treats ALL the water we use on the farm: it cost us something like $20,000 to install ten years ago.
That said, there are parts of the system that do need periodic maintenance but that happens only once a year or less. We have not yet had to change out the RO membrane. With a small in-line home unit, it may need more frequent service, depending on how much water you produce with it, but I doubt it’s frequent nor expensive to maintain. The real expense is the initial purchase.
 
I have rusty metal pipes in my attic (one of them has had a slow pinhole leak into my kitchen ceiling for a year). Even so, the rust is never at a level to make it dangerous to drink, discolor the water, or have any perceptible effect on photo chemistry - except for the one time we had to drain and replace the water heater - it came out brown for a second then. I did have it tested for lead by a lab. We haven't fixed them yet because the whole house plumbing needs to be replaced, with walls torn open.
 
vicb said:
I just want to ask whether it’s very costly to change the filters and how often it needs to be done (approximately), because I’ve heard a couple of different versions.
Click to expand...
The pre filters are cheap if you don't buy a system that uses the bespoke types.
They cost something like $3-4 a piece (there are usually 3 - two sediment and one carbon).
It is usually advised to change these every 6 months but it highly depends on the quality and amount of the water you send to it.
I feed my system good drinking water quality but it is very hard (350-450ppm) I use 3 gallons filtered water a day and I change the pre filters once a year.

In some cases you may want to change them every 3 months or add more pre filters if the input water is very poor.

This is done primarily to protect the RO membrane.
The RO membrane can usually be used for 3-5 years without problems if you remember to replace the prefilters as perscribed.
The 600GPD membranes I have used in the past cost around $150.

You can buy a cheap PPM meter and measure on occasions to see if all is OK. I replace every 5 years event if the quality is not degraded.

Post RO membrane filtering may be necessary if needed for consumption: Carbon filter and a mineral filter to reintroduce minerals into the water.
These things are not necessary for process water (and you definitely don't want to reintroduce minerals for photo usage).
If you require 0 ppm (you don't for photo processing) then you would add a resin filter after the RO membrane.

A last remark. RO water is RO water or 99% pure is 99% pure.
Everpure and BWT and others sell their solutions as if they do something magical. It is not.
In a commercial context where support is critical, it may make sense to use the branded supported solutions, but the many Korean and Chinese solutions with a lot of plastic and tubes works just as well - if you open one of the nice looking Everpure or BWT boxes you'll see much of the same inside.

If looking at a system you will want to see not only to see if it delivers the amount you need: 600 Gallons pr day is MAX 600 gallons in 24 hours - (if you need it to deliver 30 gallons in one hour, then 600GPD it is too small) but also how long the system needs to run continuously.
The motors that push the water through the system are usually not designed to run continuously. It may need a break after 15 minutes for example.
In other words, you need to be careful when you select the correct size of the system.
 
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RO is fine. If you're concerned about the effectiveness of your system, you can purchase a meter to read PPMs.
 
I have used a RO system for over 20 years. I have a system for drinking water, coffee etc, and an identical system for my darkroom. Water quality where I live suffers from time to time, constant to development etc.

My system has 5 stages, first 3 are for sediment, carbon block for removing organics and reducing chlorine then the RO membrane. After the RO membrane water is stored in a tank. When drawing water from the tank water passes through a final carbon "polishing" filter to assure taste. I usually replace the 4 filters every couple years. RO membrane is pretty much permanent.

As noted most city water is perfectly fine for everything, that's how it was where I grew up.

It's not that way where I'm at now, safe to drink but taste is awful. Loaded with calcium.

I stopped by a friend's house this week who lives in my old neighborhood in Cedar Rapids, I went to the kitchen and got myself a glass of tap water, delicious!!
 

every place ,I've ever lived so farclaimed to have the best water on earth.
 
@RalphLambrecht that says more about whom you've been talking to than about water quality. Plenty of people have a realistic outlook on what comes out of the tap, although most people only have a vague awareness of the quality parameters, especially beyond hardness.

Please note also that in the post you quoted from me, I said that Paris tap water will be fine for mixing commercial photochemistry with. It should not be misconstrued as a comparative statement about water quality in relation to other places. I effectively say "it will be sufficient for the purpose".
 
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