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Why pH of drinking water remains 7 after demineralizing?

March 13, 2008

I am an environmental enggr working in a battery manufacturing company.I had a doubt why the pH of DDW and DM water is observed as <7.The answers discussed here( Because of CO2 dissolution and formation of bicarbonates and carbonates) are satisfying. But I have a doubt why the drinking water (which is also equally exposed to atmosphere) does not change its pH? please give me an answer.
Thanks in advance.

ARYA.R Nair
Industrialist - Bangalore, Karnataka, India

Because it is already fully exposed to the air and thus CO2. Additionally, various elements/compounds in the water will for buffers that are stronger than the CO2 buffer that is formed, the higher pH.

James Watts
- Navarre, Florida
March 14, 2008

In a simple way, tap water has enough dissolved substances that it isn't ready to accept CO2. DM water has been almost depleted of those substances and is eager to dissolve whatever is more available, like CO2 from the atmosphere. That's the reason why it is highly corrosive to metals and not safe to drink.

Guillermo Marrufo
Monterrey, NL, Mexico
April 1, 2008

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