It's cheaper to buy it - the distilled water sold in the supermarket for
around 79 cents per gallon jug is good enough for most photographic
purposes. Some even have analyses of impurities; copper may be one of them,
and may make the water unsuitable for some processes. But I use this
"cheap" distilled water extensively (it's sometimes specialed at 2 for $1).
Yes, the water from a dehumidifier is "distilled" water, but it also
contains molds, fungus, dust, bacteria, and other baddies from the
surrounding air. (You can test this for yourself without a microscope:
collect a liter/quart or so in a bottle, and let it stay for a couple of
weeks: the bottom will grow whole colonies of the organic baddies.) You can
boil it to kill the living material, but that won't get rid of the dead,
dust, and other particles.
Sil Horwitz, FPSA
Technical Editor, PSA Journal
silh@iag.net
Visit http://www.psa-photo.org/