Re: R/O water dangerous?

George and others,

I don't know if I would refer to myself as an expert, but I have had a TFC
(Thin Film Composite) Reverse Osmosis filter for a number of years and can
vouch for the fact that it CAN be dangerous to drink (and I suppose, use in
an aquarium).

My R/O unit is mounted on the wall next to the kitchen sink and is not
permanently plumbed into the waterline - it uses an attachment to snap onto
the faucet. To store the water temporarily, I keep an empty 15 gallon,
all-glass aquarium on the counter, shoved back in a corner, to hold the
water until I need it. The TFC unit, as another poster has noted, removes
all of the chlorine from the water prior to sending it throught the
membrane. The R/O water from the TFC type unit is generally purer than that
produced by the CTA units but for long term storage (and especially for
human consumption) should be kept refrigerated. Without any chlorine in the
water there are enough residual minerals left in the water to allow for the
growth of bacteria.

This past summer I was out of town for a month on vacation. I had left
about 10 gallons of R/O water in the holding tank when I left (it is
covered). When I returned, the tank had a very noticeable layer of slime on
the inside glass. It wasn't algae (it was white) and I didn't wait around
to figure out what else it might be - I bleached the tank. There ARE
bacteria that can even survive chlorine bleach so I would advise people to
be careful. I have no idea if this stuff was dangerous, I certainly wasn't
going to use either myself or my fish as test subjects.

B.T.W., while I was away I had removed the membrane from the filter unit,
sealed in wet in a plastic bag and put it in the refirigerator to avoid any
possibility of bacteria growing on the menbrane.

For me and my fish, Reverse Osmosis water has been a godsend, but it has to
be handled properly (storage in sterile, opague containers).

James Purchase
Toronto, Ontario
jpp at inforamp_net