> This is an interesting thread but so far no-one seems to have
> mentioned de-ionisers. I'm not refering to water softeners which
> usually need salt (NaCl) to regenerate, but other ion-exchange
> units, many of which are a simple 'use-once-and-throw-away' style
> cartridges. Much of the water sold for topping-up car batteries
> seems to be processed in this way now.
I forgot to mention those--the CP that I have at work (a university) are
maintained entirely on DI water, which goes through a set of "zeolite
resin" columns. My understanding is that such columns are available for
lease (exchanged when saturated). The plants watered with DI seem to do
just as well as those on rainwater and RO water at home. Incidentally, a
source of small but regular amounts of distilled water at home during the
warm months is a wall or window air conditioner--the water that drips out
of these is pretty pure, and seems OK for the plants. And while we're at
it, I know all of you own a little pocket pH meter, right? If you don't
these are available for $50-60 from Fisher Scientific and many others and
are exceptionally handy. Be sure to get one that is accurate to 0.1 pH
unit. Good. Now that that's out of the way, be sure to get a hand-held
conductivity meter too, one that measures in the lowest ppm range (starts
at 0, preferably with a resolution of 1-2 ppm), typically available for
$50 or so. This will tell you if your water is pure enough for CP. If
you get any conductivity at all (i.e., more than "0" on the display), you
know there are ions in the water. You don't know what ions, but it
probably doesn't matter--you don't want to use the water if it has much
conductivity. Especially handy for testing water from mountain springs,
of which there are legions in northern California, but the water from
many is quite hard--I keep the meter and some gallon jugs in the car when I
travel.
Sean Barry
I couldn't possibly get flamed for this.