The pH of mQH2O - why is it acidic? (Jan/27/2007 )

Is the pH of mQH2O around 5.0 because of something in production or is it due to the bicarbonate reaction or something else?

The pH of pure water in gaseous equilibrium with air is 5.65. See the discussion here for example:
http://www.chem.usu.edu/~sbialkow/Classes/...nic%20Acid.html

In general, the pH of pure water is very poorly controlled. Micromolar or even nanomolar amounts of virtually any ionic compound will dramatically change its pH. There is a reason we use buffers in biochemistry.

Cheers phage, top link, great forumite.