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Water Quality/Using Citric Acid Dosing to Reduce Water Hardness


QUESTION: If you add Citric Acid to hard water would it react with the calcium to reduce the hardness? From what I understand hard water it usually higher pH due to dissolved calcium so if you lowered the pH wouldn't the calcium react with the acid? Would this not result in lowering the calcium and therefore lower the hardness?  Would any gasses be produced or precipitates that would need to be vented out or filtered?

To answer your question - yes.  Without getting into a lot of chemistry here citric acid is what is called a "chelating agent."  A chelating agent is usually an organic compound (as is citric acid)and according to ASTM-A-380, are chemicals that form soluble, complex molecules with certain metal ions (in this case Calcium), inactivating the ions so that they cannot normally react with other elements or ions to produce precipitates or scale. It also lowers the pH. Here is the web site of a company that offers a product using this kind of technology:

There are other companies that manufacture and sell these products.  I am using this one as an example and I am not recommending or endorsing this particular company over any others.

Chelation does not form gasses or precipitates, rather the chemistry of chelation acts to keep the metal ion in "suspension" or makes it more soluble so that it does not precipitate out of the solution to form scale on surfaces.

In my experience these kinds of systems are only moderately effective.  They are more effective in areas where the water hardness is less than 30ppm.  It is also very dependent on other factors in the water like alkalinity, pH, TDS, chloride, sulfate, and Magnesium.

Let me know if you have additional questions.

Steve Young
Environmental Engineer
General Contractor

---------- FOLLOW-UP ----------

QUESTION: Thanks Steve,
Keeping the Calcium out of the water heater and off my jelly and tomato jars when I can is the goal. The NuvoH2O infomercial is what got me thinking about the idea. I was thinking of just putting a venturi type feed system of some sort in just past the regulator and feeding in a liquid mixture of citric acid.  I have a good pH meter I can use to check with so I can adjust the pH to round 6.5. I would assume the pH of the water coming in to be "fairly" stable so feeding just based on flow (as a venturi does)once I figure out the dosage should be ok? I assume that you buy Anhydrous Citric Acid and mix with water? I figured I could adjust the dosage with the concentration of this mixture.  I thought I could get some pH sticks to do spot checks after I get everything going to see if I need to adjust. Thoughts??

Hi Dan,
Sounds like a good idea to me. I see no potential harm in trying it anyway.  Even a low pH excursion won't be that detrimental since citric acid is not toxic and it is not really that corrosive, even at low pH concentrations.  Having said that I would start out slowly and lower the pH very slowly.  I agree with you that the pH of the incoming water should be stable.  Are you on a well or city water?
I think your idea about using annhydrous c.a. is good.  It's much cheaper that way and the carbon freight foot print is much smaller. I think food grade would be fine - certainly you don't need the extra expense of pharmacopeia (USP) or ACS grade.  You can play around with dosages by getting a gallon of water and seeing how much of your c.a. mixture it takes to drop the pH into the range of 6.0-6.5.
So, I think you are on the right track.  Keep me posted and let me know how this turns out.  I am very curious.  Good luck and let me know if I can help out in any way.
Environmental Engineer
General Contractor

Water Quality

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Steve Young


I will answer questions on residential water treatment, i.e. use of softeners, filters, reverse osmosis systems, disinfection, iron and/or sediment removal and other issues facing the homeowner. I have worked extensively with well water systems.


I have worked in the water treatment area for many years as a consultant and as a professional environmental engineer in the private industry sector. I have designed reverse osmosis, deionization, and water softening systems. I have also done work in water quality and stream and river remediation as it relates to the Clean Water Act.

I am currently serving as an Expert for Home Improvement, Travel (New Mexico) and Travel (North Carolina);

BS Environmental Eng.

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