water purity test - ideas/information

Discussion in 'B&W: Film, Paper, Chemistry' started by csb999, Feb 11, 2009.

  1. csb999

    csb999 Member

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    Ok smart people, I know you are out there! I am interested in assessing the purity of the water (RO) that is available to me for almost free. I'm certain that it is probably sufficient for my b/w photochemisty purposes, but it is still something that I am interested in.

    I believe that testing resistance is a good method for determining the relative amount of dissolved solids. Here are my questions: if I use a multimeter to test the resistance of the water, how far apart should the probes be? (Please note: I have not yet tried this at home, so maybe it's not important - I was just thinking about it today at work.) What are "decent" figures? 8-10 M Ohms?

    Like I said, this probably isn't super important. :smile: Just curious.
     
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  2. trexx

    trexx Member

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    How far apart how deep you place them are among many variables. A TDS tester is fairly cheep or you can just assume it is OK. I have my filters changed yearly and never get above 15ppm TDS at time of change.
    I use my RO water for my mixing. I do let it stand before mixing stock solution as I find the pH a bit high out of the tap. But this goes normal is twenty minutes.

    TR
     
  3. Kirk Keyes

    Kirk Keyes Member

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    If the pH of your tap is changing merely by allowing it to sit, then it's only reacting with CO2 from the air to lower the pH. That means there is very little buffering in your water and it's meaning it's probably pretty pure (in respect to inorganics). And that means since there is little buffering, there's really no reason to let is sit, it's fine to use as it is straight from your tap.
     
  4. Kirk Keyes

    Kirk Keyes Member

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    You can test your water conductivity to approximate dissolved solids. I'd suggest buying one of the inexpensive meters that you can find around.

    If you want to make one yourself, get some metal plates 1 cm square, set them 1 cm apart, and then use an alternating current and then measure the resistance.
     
  5. wogster

    wogster Member

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    If your on a city supply, then check with the city, often they are interested in what comes out of the tap. If your on a well supply, then check with the county or state/province to see if anyone does testing. It's not only minerals, but there are a lot of other things that could potentially get into a water supply, that could affect photographic results.