Thanks, Doc for this thread. As a carbonate chemist in my own right, it makes me insane when people try to argue water, pH and equilibrium chemistry with a mix of zero knowledge and internet bromides, often vociferously with a little ad hominem throw in. You, on the other hand, obviously know your stuff.
Here's a discussion on chloramine in the garden that raises some good points:
http://blog.pennlive.com/gardening/2007/12/chloraminetreated_water_in_the.html
A number of regular gardening sites suggest adding a few drops per gallon of humic acid supplement to neutralize chloramine. It's also worth knowing that commercial potting soils are predominantly composted wood and sphagnum, and are just loaded with humic acids already. There's always the "aquarium drops" to knock this stuff out, too.
The vast majority of public water systems no longer use straight chlorine, so the old "degassing" thing is mostly dead. Some small town systems might still do this. Most water system web sites will tell you what they do for treatment and raw sources.
Just FYI, all -- if you're getting bottled water with some PPM in it and the source is from Florida, as many are.. That PPM is primarily calcium carbonate. Same thing if you're harvesting "blue pool" water from nature, as one poster suggested. Probably not a problem..